LATENT FINGERPRINT ENHANCEMENT II: FUMIGATION TECHNIQUES

Transcription

1 LATENT FINGERPRINT ENHANCEMENT II: FUMIGATION TECHNIQUES CRYANOACRYLATE FUMIGATION Cryanoacrylate is simply a very strong glue known commercially as Krazy Glue or Super Glue. Cryanoacrylate sticks to the body oil residue found on a fingerprint, therefore the ʻgreasierʼ a suspect the better the prints that will be left behind! When cryanoacrylate begins to react with the body oil residue in a fingerprint, it leaves behind a whitish-grey film which is easily visible to the human eye, especially upon darkcolored objects. This print can not be lifted however, so forensic investigators must take a photograph of the fingerprint in order to analyze it more closely. This method is called cryanoacrylate fumigation and involves placing a small amount of krazy glue in the bottom of a glass chamber (ie. jar or aquarium). The object bearing the suspected latent prints is then suspended from the top of the chamber. The chamber is then sealed and a reaction will occur if body oil residue is present. This type of fumigation can take up to between 24 to 48 hours before results are obtained. After the reaction occurs, whitish/ gray fingerprint impression that is left behind does not have a tendency to degrade - so it lasts a long time. This methods works ideally with fingerprints that have been left upon dark-colored dense objects that have a slightly textured surface such as metals and some types of hard plastics (ie. knife handles and guns).

2 IODINE FUMIGATION Iodine in itʼs pure state is a non-metal solid that is a negatively-charged anion (I - ). As you should know, all anions are highly attracted to positively-charged cations. Within fingerprint residue, and especially within sweat itself, many sodium cations exist (Na). Sweat tastes salty because there are many sodium chloride molecules (NaCl) or within it. Sodium chloride (salt) is an ionic compound composed of a single sodium cation attracted to a single chloride anion. When iodine is exposed to this compound a single replacement reaction occurs in which the iodine displaces the chloride ions and attaches to the sodium ion to produce sodium iodide (NaI). Whatʼs cool about sodium iodide is that is a dark brown/black color, therefore when it forms on light-colored surfaces it is easy to see. This method works best to enhance fingerprints that have been left upon light-colored light weight/low density objects such as paper (ie. threatening letters, ransom notes, suicide letters, cheques, paper money) and some types of fabrics (ie. light-weight cottons, some polyesters). The method by which this takes place is called iodine fumigation. For this simple technique, a small amount of iodine is placed in the bottom of a closed glass chamber (ie. jar or aquarium). The object bearing the suspected latent prints is then suspended from the top of the chamber. The chamber is then sealed with iodine crystals inside of it and a reaction occurs if sodium chloride is present. After a reaction occurs, the object is then removed and needs to be quickly analyzed and/or photographed, as newly discovered fingerprints will immediately begin to degrade after the object has been removed from the glass chamber. However, by spraying a small amount of starch water on the print, the iodine can be made permanent - producing a purple color to the print. The color change is the result of the formation of polyiodide chains. Amylose, the straight chain portion of starch, forms helices where iodine molecules assemble, forming a dark purple color.

3 LAB 3A: CRYANOACRYLATE FUMIGATION NAME: PURPOSE: In groups of two or three, use cryanoacrylate or krazy glue fumigation to enhance a fingerprint impression left upon a dark metallic item. MATERIALS: Large bull clip Spoon Safety googles Forceps Piece of paper towel Cryanoacrylate ( krazy glue ) String Piece of aluminum foil Magnifying glass Glass fumigation chamber (ie. sauce jar) PROCEDURE: 1. Obtain your spoon and bull clip and clean them off (to remove any fingerprints that are currently on them). 2. Choose one person in your group to leave their fingerprints upon the spoon and the bull clip using their right thumb and right index finger. Have this person ʻoilʼ their fingers by rubbing them on his/her forehead or nose. 3. Carefully pick up the objects using forceps and set them aside - ENSURE NO ONE ELSE TOUCHES THEM. 4. Get a piece of paper towel and soak it with water. Place the paper towel on the bottom of the glass fumigation chamber. Also, get a small square of aluminum foil and create a small dish with it. Place it beside or on top of the piece of paper towel in the bottom of the fumigation chamber. DO NOT LET THE INSIDE OF YOUR ALUMINUM DISH GET ANY WATER IN IT. 5. Cut a piece of string cm long. Carefully string your bull clip with the prints through the string - TRY NOT TO DISTURB THE FINGERPRINTS UPON IT! Attach the spoon to the bull clip so it dangles from it. Place the string on the outside of the jar and then seal the jar so that the clip and spoon are dangling from the inside of it. 6. Allow the spoon to hang clear of the bottom of the jar. It should not be touching the aluminum plate or paper at the bottom of the jar. 7. Once youʼve confirmed that the hanging apparatus inside the jar will work, call over your instructor. He/she will get you to open your jar and he/she will place 10/20 drops of krazy glue upon the aluminum at the bottom of the jar. He/she will spread the drops around. He/she will will not place the glue in the same spot.

4 8. Once this is done, quickly seal the jar again with the same dangled apparatus you had tested earlier in steps 5 and Allow the chamber to sit until next class in a warm place (minimum hours). MAKE SURE TO LABEL THE JAR WITH YOUR GROUPʼS NAME ON IT. 10. During the next class, remove the spoon and bull clip from the jar and answer the following questions. QUESTIONS (10 marks) 1. Describe what your spoon and bull clip looked like at the end of this lab. (1 mark) 2. Were you able to actually see & identify a fingerprint pattern after this procedure? Explain why or why not. If possible, identify the print pattern(s) that were made visible. (1 mark)

5 3. Why do you think that the results of this lab are not instantaneous - why do you have to wait? (2 marks) 4. What is a scientific explanation for the fingerprint enhancement upon the objects in question? (2 marks) 5. Name 3 realistic crime scene objects that the cryanoacrylate fumigation fingerprint technique works best upon? (1.5 marks) 6. Show your instructor your two fumigated objects with fingerprints on them so they can give you a mark on the space provided below. (2.5 marks)

6 LAB 3B: IODINE FUMIGATION NAME: PURPOSE: Will iodine fumigation enhance a fingerprint impression left upon paper? MATERIALS: Small piece of paper Forceps Iodine crystals Scissors Glass fumigation chamber (ie. sauce jar) Safety googles Timing device Tape Starch water PROCEDURE: 1. Worked in groups of two or three, cut a small square of fresh paper (3 cm by 3 cm). DO NOT LET ANYONE TOUCH IT. USE FORCEPS! 2. Choose one person in your group to leave a fingerprint on the paper using their right thumb. Have this person ʻoilʼ their right thumb by rubbing it on their forehead or the side of their nose. 3. Carefully pick up the piece of paper using forceps and tape it to the underside of the lid of your small fumigation chamber 4. Quickly and carefully have your instructor place 6 iodine crystals into the chamber and then put the lid on it. 5. Allow the chamber to sit aside for a minimum of 15 minutes. If you warm the chamber by leaving it near a window or holding it with your warm hands, it will speed up the reaction. 6. Once the time is up, carefully remove the piece of paper using forceps and have your instructor spray a small amount of starch water on the print and let it dry. 7. Place the dried print under question 1 on the back of this page. 8. Repeat steps 1-7 for each member of your group. 9. Once all members of your group have obtained their prints - let your instructor help you put the iodine crystals back into their original container. 10. Clean up your lab area and put back all used equipment. Answer the questions of the following page.

7 QUESTIONS (10 marks) 1. Describe what your paper sample looked like at the end of this lab (attach the paper in the space provided below). (2.5 marks) 2. Identify the fingerprint pattern made visible by this technique. (1 mark) 3. If a suspect has not rubbed his finger on his forehead before leaving a fingerprint at a crime scene, do you think his fingerprint can still be detected using the iodine fumigation method? Why or why not? (1 mark)

8 4. What scientific explanation exists for both color changes of the paper sample (the first one with the addition of iodine and the second with the addition of starch water)? (3 marks) 5. Why do you think the results for this lab are not instantaneous? (1 mark) 6. Name three realistic objects found at a crime scene that the iodine fumigation fingerprint technique would work best upon?. (1.5 marks)