C.S.I: Calculating Splatter Information A Forensic Blood Analysis of Drop Height Diameters, Satellite Numbers, and Finger Development.

Transcription

1 C.S.I: Calculating Splatter Information A Forensic Blood Analysis of Drop s, Satellite Numbers, and Finger Development. Mayson Husband, 9 th grade, Latta Junior High Respectfully Submitted to the Oklahoma Junior Academy of Science Abstract The purpose of this experiment was to examine how drop height and type of surface affect blood splatter diameter, number of finger extensions, and number of micro droplet satellites formation. It was hypothesized that as height increases, blood droplets will produce larger diameters, more fingers, and greater numbers of droplet satellites. Also, it was hypothesized that the type of surface material will cause significance variation in these characteristics. Seven different surfaces (Resin, Ceramic tile, Asphalt tile, Wood, Glass, Sheet Rock, and Concrete) were tested by dropping synthetic blood from six different heights (15 cm, 30 cm, 45 cm, 90 cm, 105 cm, and 120 cm). In general as the drop height increased the splatter diameter did also, but not in every case (from 10.8 mm at a height of 15 cm up to 14.8 mm at a height of 120 cm). The Resin surface produced the largest mean diameter at 15.7 mm and Wood produced the lowest, 9.5 mm. As the drop height increased the number of fingers did also, but not in every case either. The mean finger development for all surfaces combined increased from 0 at a height of 15 cm up to 3.2 at a height of 120 cm with the Sheet Rock surface at 5.8 fingers where Asphalt Tile produced the lowest, 0.8. The mean number of satellites also increased with height (from 0.1 up to 6.3). When all surfaces were compared, the Resin surface produced the highest mean with 4.1 satellites. The fewest number of satellites was produced by the Concrete surface with a mean of 1.7. Introduction Bloodstain Pattern Analysis is one of several specialties in the field of forensic science. Studying the drops of blood at the crime scene can help the investigators determine what must have happened during the crime and the characteristics of the person who committed the crime. The use of bloodstains as evidence isn t new, however the application of modern science has brought it to a higher level. New

2 technologies and advancement in DNA analysis are available for detectives and criminologists to use in solving crimes and apprehending offenders. Blood splatter evidence plays a key part in forensic science in forensic analysis. Actually, it s called Blood Pattern Interpretation. Herbert Leon MacDonell is the leading authority on blood stain interpretation. It was his observations that lead the way. In his published study, he gives the following tips to investigators: It is possible to determine the impact angle of blood on a flat surface by measuring the degree of circular distortion of the stain. In other words, the shape of the stain tends to change depending upon the angle of impact which caused the stain. For example, the more the angle decreases, the more the stain is less circular and longer. (2) Surface texture is one of the key components in determining spatter type. By this, MacDonell means that the harder the surface is, the fewer spatters will result. It is therefore extremely important to duplicate the surface in a controlled test. When a droplet of blood hits a surface which is hard as well as smooth, the blood usually breaks apart upon impact. This in turn causes smaller droplets. The smaller droplets will continue to move in the same direction as the original droplet. It involves reconstructing the events that must have happened to produce the bleeding. It s not something that most law enforcement officials can do, it usually requires a specialist. The specialist will try to determine what the position and shape of the drops indicate. The science of physics is very closely linked to blood pattern interpretation. He/She take measurements to determine the trajectory as well as execute carefully controlled experiments. These experiments will use surface material like those found at the crime scene to try to reproduce what has happened.

3 The smaller the size of blood splatter, the greater the energy required to produce them. Low, medium, high velocity impact spatter may be identified by their respective sizes but exceptions must also one be considered. Before a drop of blood can fall, absent any other form of applied energy, gravitational attraction acting on blood must exceed its surface tension. of a large bloodstain will be of little or no value in estimating the distance a drop of blood has fallen prior to impact. When considering the shape of a bloodstain for use in calculating its angle of impact, only a sharp, well defined bloodstain should be used for measuring its width and length. Correct interpretation of bloodstain patterns must include consideration of the surface texture of the material upon which the bloodstains have been deposited. Surface tension prevents spattering regardless of the distance a drop of blood has fallen before impacting a smooth, hard surface, for instance glass. The water molecules in blood are both cohesive and adhesive so they stick to themselves as well as other materials. The purpose of this experiment was to examine how drop height and type of surface would affect blood splatter diameter, number of finger extensions, and number of micro droplet satellites formation. It was hypothesized that as height increases blood droplets will produce larger diameter, more fingers, and greater numbers of droplet satellites. Also, it was hypothesized that the type of surface material will cause significance variation in these characteristics. Procedure: Simulated blood, from Carolina Biological Company, was loaded into pipettes and suspended over seven different surfaces (resin, glass, concrete, sheet rock,

4 ceramic tile, asphalt tile, and varnished wood). The simulated blood had a density very close to actual blood. The pipettes were perpendicular to the surfaces. The tips of three replicate pipettes were fifteen cm from the surface, and then moved upward six times to 120 cm at fifteen cm increments. Single drops of simulated blood were squeezed out onto the surfaces. A ruler was used to measure the diameter of each blood droplet. The number of fingers (extensions from the main circular droplet) was counted. The number of satellites ( micro droplets which landed away from the primary droplet) were also counted and recorded. The mean diameters, number of fingers, and number of satellites were calculated for each height and record the values in the data table. Results Three different types of analyses were made. One was for diameter, one was for the number of fingers, and the other one was for the number of satellites that beyond the main droplet. Seven different surfaces were evaluated for each of these characteristics. In general, as the drop height increased the splatter diameter did also, but not in every case. The mean splatter diameter for all surfaces combined increased from 10.8 mm at a height of 15 cm up to 14.8 mm at a height of 120 cm. The Resin surface produced the largest mean diameter at 15.7 mm where the Wood surface produced the lowest at 9.5 mm. The results are seen in Graph 1 on the following page.

5 Graph 1: In general, as the drop height increased the number of fingers did also, but not in every case either. The mean finger development for all surfaces combined increased from 0 at a height of 15 cm up to 3.2 at a height of 120 cm. The Sheet Rock surface produced the largest mean finger development at 5.8 fingers where the Asphalt Tile surface produced the lowest at 0.8 fingers. These results are seen in Graph 2.

6 Graph 2: In general as the drop height increased the mean number of satellites did also (from 0.1 up to 6.3). However, at the 120 cm height the mean dropped back to 4.5 satellites produced. When all surfaces were compared, the Resin surface produced the highest mean number of satellites with 4.1 satellites produced. The fewest number of satellites was produced by the Concrete surface with a mean of 1.7 satellites. The results are seen in Graph 3. Data tables are found in the appendix section of this paper.

7 Graph 3: Analysis and Conclusion The results of this experiment supported the hypotheses even though there was not a perfect linear relationship between the drop height and the three tested factors of satellite formation, diameter, and finger development. When the trend lines and slopes were analyzed for each characteristic there was a stronger relationship between the satellite formation and the drop height (m=1.83). The next strongest correlation was the splatter diameter (m=1.41), and the least strong relationship was finger development (m=0.38). The mean diameters increased by 37% from 10.8 mm at 15 cm to 14.8 mm at 120 cm. The mean diameters produced by the Resin surface were 65% larger than the mean diameters produced on the Wood surface.

8 Most likely the results were caused by the variations in the characteristic properties of the seven different surfaces. When evaluating the surfaces, they varied in porosity, hardness, and smoothness. Hard and smooth surfaces produced more satellites. Porous materials produced greater numbers of fingers. The results of this experiment can be important in crime scene investigations. Blood splatters can provide information about the position and identity of the perpetrator of the crime. It would be good to analyze blood splatters at different temperatures, on more surfaces, and at different angles. References 1. Blackwell, B., Christner, K., Gamer, C., and Kelley, J. Physics of Bloodstains at a Crime Scene retrieved from the internet at: 2. Forensic Fact Files, Bloodstain Pattern Analysis retrieved from the internet at: BloodStainPatternAnalysis.html 3. Bloodstain Pattern Analysis. Retrieved from the internet at: 4. BCSO - Identification Division - Blood Spatter - General Information.htm 5. BCSO Identification Division - Blood Spatter Terminology Page.htm 6. Blood Spatter Analysis Lab.htm 7. Benecke, M. and Barksdale, L. Distinction of Bloodstain Patterns from Fly Artifacts. Forensic Science International, 137 (2003),

9 Acknowledgements Thanks go out to the following people: Mrs. Stevens for her hours spent at the school helping me finish my project, my mom for her patience during science fair, and Joe and Laura Reed for assisting me with my board. Appendix: Data Tables Surface Fingers Resin 15 cm 12 mm cm 14 mm cm 15.7 mm cm 15.7 mm cm 16 mm cm 20.7 mm Surface Fingers Asphalt Tile 15 cm 14 mm cm 13 mm cm 14 mm cm 14 mm cm 14.7 mm cm 14 mm

10 Surface Number of Fingers Ceramic Tile 15 cm 12 mm cm 12.7 mm cm 15.3 mm cm 13.3 mm cm 14.6 mm cm 15 mm Surface Number of Fingers Wood 15 cm 6.3 mm cm 10 mm cm 9.7 mm cm 12.3 mm cm 13.3 mm cm 15 mm Surface Fingers Sheet Rock 15 cm 5 mm cm 8 mm cm 10.7 mm cm 13.3 mm cm 12.3 mm cm 13.3 mm

11 Surface Fingers Glass 15 cm 10 mm cm 10 mm cm 13 mm cm 13 mm cm 13.3 mm cm 13 mm Surface Fingers Concrete 15 cm 17.3 mm cm 13.7 mm cm 12.3 mm cm 13.3 mm cm 10.7 mm cm 12.7 mm 0 1.0