What Is Forensic Science?

Transcription

1 Top Shelf Science: Forensics BACKGROUND FORENSICS What Is Forensic Science? "Forensic" is derived from the Latin forensis, meaning a public forum where, in Roman times, senators and others debated and held judicial proceedings. Forensic science is the study and application of science to legal matters. "Forensic" is derived from the Latin forensis, meaning a public forum where, in Roman times, senators and others debated and held judicial proceedings. Forensic science and criminalistics can be used interchangeably and cover a multitude of disciplines. The first seven subjects in the list below are those most commonly applied in crime laboratories. Chemistry Biology Firearms Document examination Photography Fingerprints Computer technology Toxicology and drug analysis polygraphy Anthropology Psychiatry Odontology Enginnering Geology Entomology Physics Pathology Environmental science A forensic scientist primarily studies the different types of evidence recovered from a crime scene. The forensic scientist must be prepared to testify as an expert witness at a trial or hearing. As such, he or she presents data, evaluates evidence, and renders an impartial opinion to the court. A forensic scientist will also perform scientific research and train others in the area of forensic science. Evidence Evidence is defined as anything which is legally submitted to a competent tribunal as a means of ascertaining the truth of any alleged matter of fact under investigation before it. In other words, anything that is submitted to a court to determine whether an accusation is true. In the law, evidence can be divided into two general categories: direct and circumstantial. Direct evidence is evidence that, if true, prove a fact without any inferences; examples include eyewitness observations and/or video recordings of a crime taking place. Some evidence does not prove a fact but may be strong enough to imply a fact or event; this type of evidence is called circumstantial evidence. The greater volume of circumstantial evidence there is, the greater weight it carries. Probability and statistics come into play here. Evidence can also be classified as testimonial, physical, or negative. Testimonial evidence is evidence given by an eyewitness, usually under oath. Physical evidence is any object or material that is relevant in a crime. It can be most any tangible thing, as large as a plane, as small as a hair, as fleeting as an odor, or as obvious as a demolished federal building. 2

2 Both physical and testimonial evidence can be either direct or circumstantial. Here are examples of each: Direct testimonial evidence: under oath, a witness states that she saw the accused stab the victim. Circumstantial testimonial evidence: under oath, a witness states she saw the accused, who holding a knife, enter the victims house. She then heard screams. Direct physical evidence: A security tape shows the accused stabbing the victim. Circumstantial physical evidence: the fingerprints of the accused were detected on the handle of the knife that was used to kill the victim. Forensic scientists are most concerned with the analysis of physical evidence. Edmond Locard ( ), a French forensic scientist, espoused that there was always an exchange or transfer of material when two objects came into contact. The methods of detection may not be sufficiently sensitive, timely, or technologically advanced to ascertain its impact; nevertheless, a transfer takes place. This tenet is known as Locard's principle. Every contact leaves a trace. - Locard's Principle So, What Good Is Evidence? Physical evidence can: prove that a crime has been committed corroborate testimony link a suspect with a victim or with a crime scene establish the identity of persons associated with a crime allow reconstruction of events of a crime The Rules of Evidence define what evidence is acceptable (admissible) and how it can be used for the jury. Most of all, evidence must be relevant, meaning it must prove something (probative) and address the issue of the particular crime (material). Evidence is admissible if it is reliable and the presenter of such evidence is credible and competent. Generally, hearsay is inadmissible in criminal court because it is not reliable nor was it taken under oath and therefore does not allow for cross-examination. The presenter of scientific evidence, the expert witness, must establish her credibility through credentials, background, and experience. Two legal decisions have largely governed the admissibility of scientific evidence: the Frye standard and the Daubert ruling. According to the Frye standard (Frye v. United States, 1923), the interpretation of scientific evidence must be given by an expert witness and have gained" general acceptance" in the particular field of study. To meet the Frye standard, the court must decide if the questioned procedure, technique, and principles are generally accepted by a meaningful segment of the relevant scientific community. This case does not offer any guidance on reliability. Two legal decisions have largely governed the admissibility of scientific evidence: the Frye standard and the Daubert ruling. 3

3 The Daubert ruling (Daubert v. Merrell Dow Pharmaceutical, Inc., 1993) stated that the Frye standard is not an absolute prerequisite for admissibility of scientific evidence. This rule applied only to federal courts; however, states were expected to use the decision as a guideline in setting standards. The trial judge must assume responsibility for admissibility and validity of evidence presented in his court. Guidelines offered for judgment include the following: 1. The scientific theory or technique must be testable. 2. The theory or technique must be subject to peer review and publication. 3. Rate of error or potential errors must be stated. 4. The technique must follow standards. 5. Consideration must be given as to whether the theory or technique has attracted widespread acceptance within a relevant scientific community. The Daubert ruling came about in response to a rapidly changing technological society. For new theories or techniques (such as DNA fingerprinting), unacceptable delays in admitting reliable evidence led to the decision. Individual vs. Class Evidence The best evidence is the type that can be individualized to a single, specific source, so that there is no doubt as to what the source of the evidence is. This type of evidence can place a suspect at a crime scene, associate a suspect with a victim, and sometimes even prove who committed a crime. Human characteristics that can be linked to or individualized to a particular person are fingerprints, DNA, handwriting, and voiceprints. The forensic scientist is always trying to individualize evidence so that it will have more value in the case. If this is not possible, the evidence may be found to be consistent with a particular source. This is called class evidence. Class evidence alone may not be very convincing in a crime, but if there are many different types or pieces of class evidence, the value can be considerable. Examples of class evidence are hair, fibers, soil, and glass fragments. Class evidence is associated with a group. Individual evidence is linked to a particular source. 4

4 For example, a tuft of fabric is found at a crime scene. It can be identified by chemical methods as to what type of fabric it is. Suppose it is found to be a polyester. Is this information helpful? Further examination can classify the fabric as part of a blue polyester shirt. A particular suspect may own a blue polyester shirt. But how common is this? Now suppose the fabric were ripped from the suspect's shirt in a large enough piece so that it can be matched exactly to the hole in the shirt, like a jigsaw puzzle. The piece of fabric is now uniquely associated (individualized) to the suspect's shirt. Class evidence is associated with a group or class, like polyester or blue polyester shirts. Individual evidence can be linked to a particular source with a high degree of probability, like matching the torn fabric to the shirt. Individualization always involves a comparison. 5

5 Characterizing Your Shoes Identification and Individualization Complete the following in your bound journal. 1. What are some class characteristics of the shoes you are wearing? Note color, size, brand, length (in cm), and at least one other class characteristic. 2. How can you individualize your shoe using characteristics that will link them to you and to nobody else -- regardless of whether someone else s shoes have the same class characteristics? Use a photo of your shoe to identify at least two such points of individualization. Individualizing Pieces of Paper The scraps of paper in the baggies were originally five index cards that were torn in half and shuffled. Examine the torn edges using a hand lens or a DinoScope. 3. Attempt to match all five pairs of cards; record the identifying letter/number of each pair. 4. Of the five pairs you identified in step 3, identify the one pair that you are most confident match. Take a photograph of the torn side of each of the two pieces side-byside. Download the photo to a computer and transfer them onto a document. Then, add at least three points of identification that lead you to believe the two halves match (see the example on the following page). Write a short but descriptive summary paragraph below the photo. Print a copy for each member of your group, and glue it into your bound journal. 5. Choose two pieces of paper that do not match. Take a photograph of the torn side of each of the two pieces side-by-side. Download the photo to a computer and transfer them onto a document. Then, add at least three points of identification that lead you to believe the two halves do not match (see the example on the following page). Write a short but descriptive summary paragraph below the photo. Print a copy for each member of your group, and glue it into your bound journal. Conclusions 1. Do the tear patterns individualize the pieces of paper? Explain your answer. 2. Would individualization be possible if a piece of paper was torn into three pieces and the center piece was destroyed? Explain your answer. 3. What would you expect if pieces of paper were cut with scissors rather than torn? Would individualization be possible? Explain why or why not. 4. Imagine that the evidence you were examining were scraps of fabric that were cut with scissors. Would it be more or less difficult to individualize the pieces? Explain why. 6

6 Evidence Comparison Examples MATCH The photo above shows paper piece 2A on the left and 2F on the right. These two edges appear to be the boundary between a single tear because there are several distinctive edges that match up. All four labeled positions (A D) have a protrusion on the left piece, and a corresponding indentation on the right side, at the same position form the end, and with same approximate size. Additionally, the overall width of both sheets of paper were identical (measured as 5.35 cm). This circumstantial evidence leads me to believe that these two pieces have been individualized to a single sheet of paper. ***************************************************************************** NO MATCH The photo above shows paper piece 2A on the left and 2D on the right. The overall width of both sheets of paper were identical (measured as 5.35 cm). However, these two edges appear to be distinctly different from each other. For instance, Positions E and G each show a indentation, but the other piece of paper has no corresponding protrusion at that position. Position F shows a notch with no corresponding protrusion. 7

7 Probability and Statistics "The probability of showers Tuesday is 80%." "The odds of the Detroit Tigers winning two consecutive baseball games is 20 to 1. The likelihood of winning the lottery is 1 in 250,000." "The frequency of death in an auto accident is " We deal with probability most every day in one form or another. The law does as well: "probable cause," "probative," "probability of an accidental match," "weight of evidence," and "beyond a reasonable doubt" are all probability terms used in our legal system. Can evidence be quantified? Can evidence be valued numerically, like odds at a horse race? Probability (P) is the likelihood that a certain event will occur. If P = 0, the event will not occur; that is, it will occur 0% of the time. If P = 1, the event will definitely occur; that is, it will occur 100% of the time. Probability is calculated as a ratio of the number of actual occurrences to the total of observations. So, for example, assume your class has 24 students. The probability of someone wearing something red in your class may be 6 out of 24, or 1 out of 4. So, Probabilities are often reported in decimal form by multiplying by 100. So, the probability of someone in your class wearing red is (.25)(100) = 25%. If there are 850 students in your school, how many of those students should be wearing something red? Statistically one of every 4 should be wearing something red, so: (Probability in decimal form) x (Population) = (Number of Occurrences).25 x 850 = 213 So, statistically, there should be 213 students in the school wearing something red. Let s try another problem: A different class in your school has 19 students (your school still has 850 students). Only two students in that class are wearing something yellow. Calculate the probability of a student in that class wearing yellow, and determine the number of students in your school wearing something yellow.* Wearing something red or wearing something yellow are examples of independent events, which are events that are independent of other events. Probability is the likelihood that a certain event will occur. 8

8 Now, let s assume both red and yellow fabric were found near some graffiti in the school bathroom, and you are asked to determine the number of students in your school wearing both red and yellow. To do this, multiply the probabilities of each independent event: (P of wearing red) x (P of wearing yellow) = (P of wearing red AND yellow) Dividing 2 by 76 gives the probability of finding a student in your class wearing red and yellow as P =.026, or 2.6%. Please note, this method works ONLY if the events are independent! If, for instance, people who wear red are likely to also wear yellow because the two colors are complimentary, then you would need to introduce more complex statistical procedures. In this course, though, we will deal only with independent events. Practice: How many students in your school (850 students) would be wearing BOTH red and yellow?** These probabilities are gained statistically. You may find that there are more or fewer students wearing a combination of red and yellow. The Rule of Large Numbers says that the larger the population, the more likely that the actual numbers will approach those of the computed probability; that is, the larger the population you are considering the more likely your calculated number of occurrences will be correct. Correctly calculating probabilities is critical to making a strong case in court; many cases have been thrown out of court or lost because the computed probability of a random match of evidence has been overestimated. Answers: * P = 2/19, or.105, or 10.5%; 89 students ** 22 students 9

9 Probability and Statistics Complete the following in your bound journal. 1. Usually, evidence is used to link or associate a suspect to a crime. More often than not, the evidence is class evidence. For example, a blue fiber is found at a crime scene. Look at your classmates; how many could have transferred a blue fiber from the clothes they are wearing? How many suspects, then, are in your class? 2. Suppose the entire student body (650 students) had access to the crime site. How many suspects would there be based on the statistics from your class? (Clearly show all relevant calculations!) Is the blue fiber evidence of value? That is, does it do a good job of reducing the number of suspects down to a small number? 3. Suppose that along with the blue fiber, an orange fiber was also found. Does the combination of a blue fiber and an orange fiber improve the evidentiary value? Explain why. (Clearly show all relevant calculations!) 4. Does the number of characteristics of a material and/or the number of different, relevant objects found at a crime scene improve the probability of matching the evidence to a single suspect? Why or why not? 5. Camden has the following demographics: Female residents 2206 Male residents 1787 Unmarried residents 1712 Asian residents 20 American Indian residents 2 Caucasian residents 3937 a) A suspect is described as a male, Asian resident of Camden. How many people fit that profile? Would that characterization be of value? b) A suspect is described as a female, married, and Caucasian. How many people fit that profile? Would that characterization be of value? 10

10 Hair as Forensic Evidence What Is Hair? Hair is a filament composed mostly of keratin, a tough protein polymer of amino acids that makes the hair strong and flexible. Hair is produced in a bulb-shaped pocket in the skin, called a hair follicle. At the end of the follicle is a network of blood vessels called the papilla that supply nutrients to the hair and help it grow. The sebaceous gland secretes oils to the hair to keep it conditioned. Above the follicle is the hair shaft, which is made of dead cells. Why DO We Have Hair? Hair provided our ancient ancestors with insulation to protect them from extreme temperatures as well as from harmful sun rays. It may have even served as camouflage, as it does in many animals. These days, we have clothes and sunscreens; however, 80% of lost body heat is through the head, so a good crop of hair can act as an insulator. Hair at specific places on the body has a specialized purpose; for example, hair in our nose and ears acts as a dust filter; eyebrows were meant to shield our eyes from excessive sunlight and block sweat from our forehead. What Attributes of Hair Make It Useful in Forensic Science? There are about 100,000 scalp hairs on the average person. At any one time, % are growing; the remaining are in the process of separating from the hair follicle and eventually falling out-at a rate of about 100 a day. Not only is hair common, but it is quite durable and is resistant to physical and chemical degradation. It is also persistent in that it tends to cling to things, such as fabrics. Examination of hair cannot determine sex or age. However, new laboratory techniques have enabled DNA extraction from hair under favorable circumstances. Nuclear DNA can be found in the hair root or adhering tissue and mitochondrial DNA in the hair shaft. 11

11 Macroscopic Examination of Hair Complete the following in your bound journal. 1. You should have brought some of your own hair from a hair brush; if you haven t, run your fingers lightly through your hair until a strand is dislodged (do NOT pull it needs to fall out naturally ). Tape the hair strand in your notebook and examine it with a hand lens. Record any characteristics that can be used to describe your hair. 2. Repeat step 1 on a strand of hair that you forcibly pull out of your scalp. 3. How can the characteristics you listed be used to exclude a person as a suspect in a crime (be specific!)? 4. What differences do you notice between the two hairs? How could the differences be useful to a forensic scientist? 12

12 The Morphology of Human Hair Structure A hair shaft is composed of three parts-the cuticle, the cortex, and the medulla. The cuticle is the clear, outside covering of the hair shaft. It is made up of tough overlapping scales, such as on a fish or like shingles on a roof. The cortex is made up of keratin molecules aligned parallel to the length of the shaft. Embedded within the cortex are pigment granules that give hair a lot of its color (black, brown, yellow, or red). Gray or white hair is the absence of such granules. The medulla is a row of cells running along the center of the cortex like a canal. It may appear dark or translucent depending on the presence of air, liquid, or pigments, and it can be continuous, interrupted, or fragmented. When the hair shaft is darkly pigmented throughout the medulla and the cortex, the pattern is said to be solid. When no medulla is present, the pattern is absent. Medulla Pattern Description Picture Continuous Interrupted or Intermittent Fragmented or Segmented Absent Solid One unbroken line of color Pigmented line broken at regular intervals Pigmented line unevenly segmented No separate pigmentation in the medulla Pigment is so dark that you cannot see the medula Forensic scientists characterize hair by measuring it medullary index (MI). The medullary index is the diameter of the medulla divided by the diameter of the hair: MI = diameter of the medulla diameter of the hair When the medulla pattern is solid, no comment can be made about MI. When the medulla is absent, an MI can still be calculated (because you will be able to see the boundaries of the empty channel). 13

13 Diameter The diameter of human hair ranges from 25 to 125 micrometers (µm). Generally, individuals have small variation within the type of hair (i.e., scalp, beard, chest, pubic, etc.). Because the diameter of a hair shaft is so small, you will need to utilize a micrometer to measure it. To do so, place the hair on the micrometer and take a photograph of it at high magnification. The width of the lines on the micrometer are.2 mm (200 µm). You will compare the width of your hair to the width of the line, creating a ratio equation to calculate the actual width of your hair: Actual width of your hair = width of your hair in the picture Actual width of the micrometer line width of micrometer line in the picture In this equation, you will measure both of the values on the right side of the equal side with a ruler. The actual width of the micrometer line is a known value 200 µm. You will solve for the value in the numerator of the left side of the equation. Tip The tip of the hair shaft will taper to a point if it has not been cut or abused for a while. Hair that has been recently cut is squared off at the tip, but within two to three weeks it becomes rounded. Frayed hair or split ends result from dryness and lack of care (no conditioners), harsh chemicals (bleaches), or overuse of a blow dryer (too much heat). Fluorescence Some hair that has been chemically treated will fluoresce when exposed to ultraviolet radiation. Fluorescence can be diminished by washing and by wear. Nevertheless, fluorescent properties are useful for comparing hairs of a common origin as well as spotting hairs for collection. Root Head hair grows at a rate of about 1 cm per month and is replaced about every 3 to 5 years with new hair. There are three stages of growth: the anagen phase (80-90% of hair follicles at anyone time); the catagen phase, which is an intermediate stage; and the telogen phase (18-10%), in which the follicle is ready to push out the mature hair. The hairs on your brush, comb, or shoulder are telogen hairs and should reflect that in the bulbous appearance of the root with little if any follicular tissue around it. Anagen hairs that have been forcibly removed from the scalp may still have follicular tissue attached and may have pigment granules evident since the hair was still growing. The hair's root is embedded in the follicle, which is in equilibrium with the body's blood supply. Whatever is taken into the body is distributed into the growing hair. This is important in analyzing hair for drugs and poisons. Since hair grows at a fixed rate, a time frame of the introduction of a foreign substance can sometimes be established. 14

14 Microscopic Examination of Hair Complete the following in your bound journal. You will examine the hair samples of all members of your group with a DinoScope. In your journal, create a table similar to the one shown below, only make yours larger, so you have room to describe your observations. Add a column for every hair sample you observe. Characteristic Your name Partner s name Length (cm) Color Appearance (straight, curly, kinky) Diameter Medulla Type Calculated MI Tip Appearance under fluorescent light Cosmetic treatment (yes or no) Procedure 1. Measure and record the length of your hair sample. 2. Record the color and appearance of your hair sample. 3. Place the hair sample on a microscope slide with a micrometer and add a drop of mineral oil or glycerin. Anchor it with a cover glass. 4. Start with the lowest magnification of the microscope. Take picture of your hair, being sure to include both a micrometer line and the hair in the picture s frame. 5. Calculate and record the diameter of your hair. Clearly show your calculations. 6. Go to high magnification and focus. You need a to be viewing a length of the hair that clearly shows its characteristics; find one by pulling the hair strand through the liquid under the cover glass. Change the light to be sure you are seeing the medulla, if there is one. 7. Photograph the hair under high magnification (so that you will be able to measure what is necessary to calculate MI). 8. Identify the type of medulla. 9. Calculate the medullary index (MI). Clearly show your calculations. 10. Examine and identify the appearance of the tip of your hair sample. 11. Examine the hair under fluorescent light. Record whether or not it glows. Add to the photos you ve taken so far so that you have in your journal - pictures of at least 3 medulla types, at least 3 hair colors, and at least 3 types of tips. Label each of these! (Proceed to the next page!!!) 15

15 Other Observations 12. If neither you nor any of your partners have dyed hair, complete steps 3, 4 and 11 on a hair strand that has been dyed. Repeat with a sample of bleached hair. 13. Pluck a hair from your eyebrow, eyelash, arm, or other part of your body. Complete steps 3, 4, 7, 8, and 9 on this hair. 14. Examine the root end of your hair samples under magnification. You should look at an anagenic root that was forcibly removed and a telogenic, mature hair root that you obtained by combing or brushing. Take a picture of each. The Cuticle The cuticle of human hair is difficult to observe under a microscope because it is close-packed, transparent, and fine. Its structure can be delineated, however, by making a cast of hair. 15. Clean a strand of your hair by pulling it through a folded tissue moistened with alcohol to remove grease and oil. 16. Place a thin coat of clear fingernail polish on a microscope slide and press your hair into it. 17. After the polish becomes sticky but not dry, remove the hair and examine the cuticle impression at high magnification. Take a picture of what you observe. ** Note: Casting hair is somewhat difficult; if you make a very good cast, please label the slide with the identity of the animal and SAVE it for others to observe, should they NOT be able to properly cast their samples. Conclusions 1. Be sure all required pictures have been cut out and pasted in your journal! 2. Based on your observations, how can you tell that a hair has been dyed? Bleached? 3. Compare the pictures of your hair and one of your partners hairs. Identify and write about the similarities and differences. What significance does this have? Be sure there are pictures of the two hairs in your journal. 4. Compare the pictures of the hair you observed in step 13 in the Procedure section to your scalp hair. Identify and write about the similarities and differences. What significance does this have? 5. Describe the differences you observed in pulled hair vs. hair that falls out naturally. 6. What determines whether hair evidence is class evidence or individualized evidence? 16

16 Animal vs. Human Hair Complete the following in your bound journal. The first question asked in studying hair evidence is whether it is human or animal hair. It is estimated that there are 70,000,000 cats in the United States, 60,000,000 dogs, and millions of other domesticated animals. The following lab will explore how animal hairs differ from those of humans. Your goal is to discover differences in characteristics that will allow you quickly and effectively determine whether a hair is human or animal. Procedure 1. Complete the observations you made for human hair in Microscopic Examination of Hair (Steps 110 on page 16) on samples of hair from two animals (excluding deer hair), being sure to note the animals involved. Because the animal hairs have been permanently mounted on microscope slides, you do not have to complete step 3 of the procedure. To photograph the animal hair with a micrometer, place the animal hair slide on top of the micrometer slide. 2. The sample of deer hair clearly shows two features of hair: - Observe and describe the color of the hair along the length of its shaft; - Observe the hair under a Dinoscope; in this case, you will be able to see the cuticle very clearly. Describe, draw, or photograph the pattern of the cuticle. Conclusion 1. Be sure all required pictures have been cut out and pasted in your journal! 2. Explain how a forensic scientist can distinguish whether a hair found at a crime scene is human or animal. Be as specific as possible. 17

17 Hair Unit Final Conclusions Hair is considered class evidence in forensic science. Depending on the circumstances, its evidentiary value or importance is based on statistics. What are the chances that a hair came from a suspect or a victim? If there are only three possible suspects, a blonde, a brunette, and a redhead, and the circumstantial evidence consists of a red hair, then there is a 100% probability that the redhead committed the crime. However, if all three suspects have red hair, then the probability of choosing the perpetrator is one out of three. Not good enough! In this case, one would hope for more hair characteristics, or other circumstantial evidence. As you learned earlier, as the number of characteristics or objects linking a suspect increases, so does the probability of association or involvement. 1. A class has the following makeup: Hair Color Girls Boys Blonde 6 4 Brown 4 7 Red 0 1 Black 6 2 a. A red hair is found at a crime scene. Calculate the probability of this characteristic in this class. b. A black hair? c. If 75% of students in this class have short hair, what is the probability of finding the student who left a long brown hair? d. If there are 630 students in the school, statistically how many boys would have black hair? e. In this class, two blondes have a fragmented medulla and one other blond has hair longer than 50 cm. How many girls in the school would you expect to have blond hair longer than 50 cm with a fragmented medulla? 2. HINT: READ the introductory section in this workbook!! The body of a woman was found in the woods. Some hair fibers found on the body were sent to the crime lab for analysis. The ends of the hair attached to the body were gray, but the tips of the hair show it had been dyed. The distance from the root of the hair to the beginning of the dyed area measured 8 mm (.8 cm). Investigators determined that the victim s hair had last been dyed on August 1, On approximately what day did the woman die? Explain, showing your calculations. (continued on the next page) 18

18 3. A woman with long hair is a suspect in a burglary case. At the crime scene, several long hairs were found attached to a broken lock of the safe. The police obtain a warrant and request a sample of 25 to 50 hairs from this woman. They tell the woman it is important that they pull the hairs from her head rather than to merely cut the hairs. The police suspect that the woman was stealing to help support a drug habit. a. Why is it important that the police pull the hairs from her head rather than cut them? b. Why is it necessary to obtain 25 to 50 hairs from this woman? c. The woman denies that she is currently taking illegal drugs and states that she stopped using drugs about a year ago. Explain how police can determine if the woman has been off drugs for a year. d. Is the hair found at the crime circumstantial or direct evidence? Explain why. f. Is the hair found at the crime scene class or individual evidence? Explain why. 4. Someone in your class has stuck a wad of bubble gum on the teacher's desk. Embedded in the top of it is a hair. Examination finds that it is brown, 5 cm long from bulb to tip, the medulla is fragmented the shaft is 85 µm in diameter, the tip is cut, and there is no evidence of any treatment. Data was collected and analyzed from a single classroom of 23 students, as shown in the table below. Use the data from table to calculate the number of suspects in the school of 630 students. Show your work! Color Characteristic Number of students in the class having that characteristic Medulla Characteristic Number of students in the class having that characteristic Brown 13 Absent 1 Black 4 Fragmented 14 Red 1 Interrupted 6 Blonde 5 Continuous 2 Length Diameter Under 3 cm 3 under 40 µm cm µm cm µm cm 7 Over 80 µm 3 Over 30 cm Cosmetic Treatment Cut 16 Dyed 3 Split 6 Bleached 1 Frayed 1 Tip 19

19 Hair Resources Comparison of Hair Characteristics by Race Race Appearance Pigment Granules European Generally straight or wavy Small and evenly distributed Other Color may be blonde, black, red, or brown African Kinky, curly, or coiled Densely distributed, clumped, may differ in size and shape Asian Straight Densely distributed Shaft tends to be coarse and straight Thick cuticle Continuous medulla Cuticle Shapes coro nal (cro 20

20 What Is a Fiber? Fiber Evidence A filament is a single strand of material of indefinite length. A fiber is composed of many filaments twisted or bonded together to form a thread or yarn. For forensic purposes, fibers are classified as either natural (animal, vegetable, or inorganic) or artificial (synthetic). Fibers are twisted or weaved together to manufacture fabric, carpet, paper, rope, and batting. Types of Fibers Filaments Fibers Fabrics Fibers, like hair, are considered class evidence. They lack individuality because they are mass-produced in such large quantities. For example, in 2001 over 3.5 billion pounds of cotton yarn was produced in the United States! Some of this cotton was used to make 625 million T-shirts and tank tops, and 184 million jeans. The probability of finding a match of cotton fibers from a suspect's T-shirt and a victim seem horrendous. Any characteristics that aids in narrowing the origin of the fiber to a limited number of sources greatly improve the value of the evidence. Tables 1 and 2 below lists common natural and synthetic fibers that are currently in use: Fiber Table 1: Common Natural Fibers Chemical Source Description Common Uses Hair mammals protein apparel, blankets Silk insects protein Apparel Cotton plant cellulose apparel, textiles Linen plant cellulose tablecloths, napkins Rayon plant regenerated cellulose apparel, upholstery, curtains Acetate plant altered cellulose apparel, curtains Fiberglass sand silica insulation Table 2: Common Synthetic Fibers Fiber Trade Name Common Uses Acrylic Creslan, Acrilan, Orlon home furnishings, cigarette filters Aramid Kevlar protective vests, rope, sails, sporting goods Nylon Antron, Meryl apparel, household furnishings, rope, seat belts, tents Olefin Innova, Spectra sportswear, household furnishings, rope, bags Polyester Dacron, Kodel, Fortrel apparel, household furnishings, fiberfill, auto upholstery, rope Spandex Lycra, Clearspan stretchable apparel 21

21 Types of Fibers Why Are Fibers Important as Forensic Evidence? Clothing is made of fibers. Look around you - there are many types of fabric, many colors, many uses. Fibers, like hair, are easily exchanged so they can provide evidence of personal contact, and possible association between victim and suspect or object. For example, read an actual case as summarized below: Five-year-old Melissa Brannen disappeared from a Christmas party the evening of December 3,1989. The suspect, Cal Hughes, left about the same time but denied having any contact with her. A search of his car found many fibers and hairs. A few black rabbit hairs found in the car could have come from Melissa's mother's dyed rabbit coat, which Melissa was fond of playing with. When she disappeared, Melissa was wearing a Sesame Street outfit of red tights, red plaid shirt, and a blue acrylic sweater, available, in limited quantities as it turned out, only from JC Penney. Blue fibers from the suspect's car matched the only blue acrylic fiber that could be found in Melissa's room. This provided an additional association between the victim and the suspect's car. Red cotton fibers from the car matched those from a similar Sesame Street outfit. The single blue fiber from Melissa's bedroom was found to be identical to those from a JC Penney, Sesame Street blue sweater obtained elsewhere. An experiment showed that the probability of a coincidental match of the blue fibers from the car and those from the Sesame Street outfit was extremely remote. Thus, the association of fibers linked to Melissa with those found in Cal Hughes's car allowed successful prosecution of the case. Melissa Brannen's body, however, was never found. (Summarized from Fisher pp ) 22

22 Chemical Properties of Fibers Complete the following in your bound journal. Fabrics have chemical properties, determined by their chemical composition, that describe how they react when they are exposed to agents that might change their chemical composition. Such agents include acids and bases, fire, and gentle heat. Specific fibers react in characteristic ways, allowing for class identification. For example: Strong acids may cause some synthetic fibers to shrivel up; When fibers are gently heated, they often decompose to smaller molecules. For example, acetate fibers decompose to form acetic acid that turns blue litmus paper red. How a fiber burns, its odor, and the nature of its ash are specific to the types of fabric; Your goal is to devise a method of using the chemical properties of the reference fabrics to identify as closely as possible the unknown fabrics that will be provided to your group. Special Safety Considerations The chemicals you will be using in this activity involve strong acids, bases, and solvents, all of which can irritate the skin, cause irreparable damage to your eyes if not immediately washed, and may dissolve your clothing, as you will see. Wear safety glasses, gloves, and an apron. Clean up spills, even a drop, at once. Report any accidents to your teacher. Wash your hands after the lab. PRELAB - Do this at home, to save time!! You will be conducting three series of tests to distinguish the chemical properties of fibers chemical tests, a thermal decomposition test, and a burn test. For each of these, you will do a trial for each known fiber. All observations need to be recorded in your journal, in neat, well organized tables. Please construct these tables outside of class time. 1. Chemical Tests Table: you will be observing the reaction of each fiber with Acetone, 6M NaOH, and 6M HCl. So in your journal, create a data table that looks like this (only larger, so your observations can neatly be written in the cells!) Chemical Test Results Fiber 6M HCl 6M NaOH Acetone Cotton Silk Wool Acetate Acrylic Nylon Polyester Rayon Olefin 2. Thermal Decomposition Test: prepare a similar table with the following headings: Fiber Appearance of Smoke Thermal Decomposition Test Change in Lead Change in Red Acetate Paper Litmus Change in Blue Litmus Appearance of Residue 23

23 3. Burn Test: Fiber Behavior as it approaches flame Behavior in the flame Burn Test Behavior as it leaves the flame Odor Appearance of residue Chemical Tests 1. For each test, use only a few short fibers. 2. You will test the HCl and NaOH in the plastic well plates. However the acetone test must be performed in the porcelain well plates. Because acetone is very flammable, you need to perform this test far away from any open flame! 3. Arrange your samples in the well plates so that you can test each sample in each of the three reagents: acetone, 6M sodium hydroxide (NaOH), and 6M hydrochloric acid (HCl). 4. Add enough reagent to cover each sample. Use a toothpick to mush the fabric into the liquid, but be sure not to use the same toothpick in multiple reagents (that is, each toothpick should touch ONLY the HCl OR the NAOH OR the acetone). You will need to wait at least 15 minutes before you make observations; move on to another test while you wait. 5. After 15 minutes, record your observations in your table. It may be helpful to view results with a hand lens. Thermal Decomposition Test 6. Place two or three fibers in the bottom of a glass test tube. 7. Place a piece each of red litmus paper and blue litmus paper into the inside of the neck of the tube (make sure they are not on top of each other). 8. Wet a piece of lead acetate paper. Place the wet lead acetate paper over the top of the test tube, then cover it with a small round of filter paper. Gently push the filter paper down to secure it (and the lead acetate paper) in place. You can also use the test tube clamp to hold the filter paper in place. 9. Holding the test tube with a test tube clamp, gently heat the base of the test tube over an alcohol burner. Observe what happens to the lead acetate paper, the red litmus paper, and the blue litmus paper. Observe any residue and the appearance of any smoke that is emitted. Record all your observations the table. 10. Repeat the procedure for all fabric samples. Burn Test 11. Use two or three fibers that are about 3 cm long. Hold the sample at one end with tweezers and bring it slowly into the open flame of an alcohol lamp. Once it catches fire, pull it away from the flame and place it onto the glass plate. Note all of the observations you wrote in your data table. 12. Fill in your table using words such as scorches, smolders, fuses, melts, glows, shrinks, sizzles, flickers, flares, sputters, burns fast, burns slow, smoky, sooty, and so on. The ash or residue can be light gray, black, dark gray, shiny, clumpy, beady, sticky, feathery, and so on. 24

24 Conclusions 1. Explain why multiple tests of a fabric s chemical and physical properties are needed to provide class evidence that has the greatest value. 2. (Warning: this is a challenging question with more than one correct response!) Use the results of all of the chemical property tests you conducted to create a dichotomus key that can be used to identify an unknown fiber. Note: you will use the chemical properties ONLY because any single type of fiber will ALWAYS display the same chemical properties; for example, all cotton will burn in the same way. However, the physical properties of cotton can differ among fabric; for example, cotton can be woven in any of the three patterns. What the heck is a dichotomous key?? A dichotomous key is a tool that allows the user to determine the identity of items in the natural world. Keys consist of a series of choices that lead the user to the correct name of a given item. Dichotomous means divided in two parts, which is why a dichotomous key gives two choices in each part. In each step, the user of the key is presented with a statement based on the characteristics of the item; if the item s characteristics match the statement, the user is directed to one part of the flowchart; if not, the user is directed to another part of the flowchart. Ideally, the dichotomous key uniquely identifies each possible item. For example: 25

25 Physical Properties Part I: Fibers Complete the following in your bound journal. In the last activity, you used the chemical properties of fabric to help identify the type of fabric. When trace evidence is found at a crime scene, determining the type of fiber is the first step. Once forensic scientists have determined the type of fiber used in a fabric, they turn to the physical properties of the fiber and fabric in an attempt to match evidence with reference samples from suspects. A physical property is any characteristic of a substance that can be measured or perceived without changing its identity. Procedure 1. List as many physical characteristics as you can think of that could be used to distinguish a particular fiber. Then, create a data table in your journal similar to the one below (only larger!) to record the properties that have evidentiary value for each of the fibers. For instance, Property 1 might be Color ; in the case of the fabric samples provided in this lab, that would not be a physical property of value because all of the samples are the same color. Each group HAS to calculate the fibers diameters and their appearance under fluorescent light, as well as two other physical properties (that you define) which help distinguish the fibers from one another. 2. To help you collect the necessary data, observe each fiber with a low-powered Dinoscope. Place each fiber on a micrometer and take a photograph. You can then use the photos to identify all of the fibers physical properties. Physical Properties of Fibers Results Fiber (Property 1) (Property 2) Diameter Fluorescence Cotton Silk Wool Acetate Acrylic Nylon Polyester Rayon Olefin 26

26 Physical Properties Part II: Fabrics Complete the following in your bound journal. Occasionally, forensic scientists get really lucky and find an in-tact piece of fabric at a crime scene (as opposed to single fibers). As you learned in the first unit of this course, fabric can be used as individual evidence if a swatch exactly matches the parent cloth and if a torn edge fits, like a puzzle piece, exactly to the spot from which it originated. This doesn't happen very often; yet, if more than a fiber exists, the fabric itself can add to the characteristics of the evidence. Fabric is classified by its type of weave. In a weave, the lengthwise yarn is called the warp. It is usually stronger, smoother, and more even, with a tighter twist to it than the weft (the crosswise yarn). The warp need not be the same material as the weft (this would be called a blend), nor the same color. Sometimes, the warp and the weft have different diameters in order to produce special effects, such as ribbing. The three basic patterns are shown below: Plain Satin Twill The Three Basic Weave Patterns In plain weave, the warp and weft are aligned so they form a simple criss-cross pattern. Each weft fiber crosses the warp fibers by going over one, then under the next, and so on. Variations of the plain weave include bundling fibers so that two twisted weft fibers go over and under two twisted warp fibers, etc. In a satin weave, the weft fibers float over four or more warp fibers before going under one fiber and back up. The satin yarns create a more lustrous appearance and the fabric drapes better than plain weaves, but they are not durable. Twill is a type of fabric woven with a pattern of diagonal parallel ribs. It is made by passing the weft thread over one or more warp threads and then under two or more warp threads and so on, with a "step" or offset between rows to create the characteristic diagonal pattern. 27

27 Physical Properties Part II: Fabrics Complete the following in your bound journal. Procedure 1. In your journal, create a table to record the properties of each of the fabric samples you have been using in this unit. Physical Properties of Fabrics Results Fabric Weave Warp Thread/mm Weft Thread/mm Cotton Silk Wool Acetate Acrylic Nylon Polyester Rayon Olefin 2. Examine each fabric sample at a magnification that allows you to classify the weave. Be sure to check BOTH sides of the fabric sometimes the weave is easier to distinguish on one of the sides! Classify each according to the weave. 3. Measure and record the number of threads per mm in the warp and weft direction of each of your fabric samples. To do this, view the fabric with the micrometer on top of the fabric. Count the number of warp and weft fibers that fit inside one of the micrometer squares. Use the fact that each micrometer square is 2mm x 2mm to calculate the number of fibers per 1mm. Conclusions 1. Explain how physical properties of both fibers and fabrics can aid a forensic scientist in matching evidence to a suspect. 2. A single fiber is found at a crime scene and found to match the physical and chemical properties of the shirt that a suspect was wearing at the time of the crime. a. Is the fiber evidence circumstantial or direct evidence? Explain your answer. b. Is the fiber evidence class or individualized evidence? Explain your answer. 28

28 Putting it all Together: Identifying an Unknown Complete the following in your bound journal. Your goal is to use the chemical and physical properties you made of the reference samples to identify two unknown samples provided to you (one will be a fabric, while the other will be a fiber sample). Be sure to record what you are doing, the order you are doing it, and the results in your journal. Record the sample numbers you receive in your journal. Begin by examining the physical properties of each unknown, including photographing the sample on a micrometer. ( It is important to do this first because the chemical properties destroy the sample you don t want to find out after doing the chemical tests that you don t have enough of the sample left to do a proper observation of physical properties. ) Use the dichotomous key you created of chemical properties to identify each unknown sample. Once you feel like you have identified your samples, compare the physical properties of each unknown to a reference sample. Ask Mrs. Damian for a reference sample of the type of fabric you believe your sample matches. Then, prepare a photo comparison (your sample compared to the reference sample you believe matches it) of each of your unknowns. Your descriptive paragraph (below the photo comparison) should clearly indicate the type of fabric and should describe the chemical and physical properties you are claiming match. 29