Trace Evidence

1. Trace Evidence Hair and Fiber Samples

2. Trace Evidence • Trace evidence is circumstantial evidence • It will not point to just one person • It can show a certain person was in a certain place. • People have been found guilty just on circumstantial evidence.

3. Forensic Examination of Hair • Hair falls from the body every day • Unless skin is attached to it, it is hard to use DNA to say whose it is. • Usually, hair is removed by force at a crime scene.

4. Morphology of Hair • Hair is made from skin cells • Hair has 3 parts – the cuticle, the cortex, and the medulla • Cuticle • Hair resists decomposition • Corpses have been dug up with full heads of hair. • It retains its structure for a long time.

5. Morphology of Hair • Cuticle = a scale structure covering the outside of the hair. • Made of overlapping scales that point toward the tip of the hair. • The skin that makes of the cuticle are covered in a protein called keratin. • Finger and toe nails are also skin cells covered with keratin.

6. Morphology of Hair • 3 basic patterns to cuticles • Coronal, spinous, and imbricate (page 413) • We use these when matching samples • Looking at the scale pattern tells us if it is human or animal. 2) Cortex • This is the main body of the shaft. • Looks like blocks stacked end to end.

7. Morphology of Hair • This is where the pigments for color are found. • How the pigments are shaped and distributed gives us points for comparison. 3) Medulla • It is a collection of cells running up the center of the hair. • In animals, it makes up ½ the width of the hair. • For humans, it is generally 1/3 or less.

8. Morphology of Hair • This percent can change from hair to hair on the same person. • The medulla can be continuous (uninterrupted), interrupted (with space between), fragmented (no real pattern) or absent. • Humans usually have fragmented or absent. • Human medullas are shaped like a cylinder.

9. Morphology of Hair • A cat’s medulla looks like a string of pearls. (page 416) • There is a database of the 35 most commonly encountered animals. 3) The root • Root contains what is needed for hair to grow. • The initial growth phase lasts 6 years • When it is pulled from the root, it will have a follicular tag

10. Morphology of Hair • We use the tag for DNA samples • Once the root stops growing, it shrinks. • The hair will last 2-6 months before it falls out.

11. Identification and Comparison of Hair • It tells us if it is animal or human • Will it match the suspect or victim • We will get samples from the scalp or pubic regions for comparison.

12. Factors in Comparison of Hair • Comparing human hairs has to be done carefully • We match color, length and diameter, does it have a medulla, and the shape and color intensity of the pigments. • Dye can be seen in the cuticle • It actually looks like another layer outside of the cuticle.

13. Factors in Comparison of Hair • Bleaching hair removes pigments and looks yellow under the microscope. • If the hair has grown, it is very easy to tell the difference between colored and natural. • Hair will also collect poison. • This is useful in cause of death. • We use a comparison microscope to look at hair samples.

14. Factors in Comparison of Hair • It is easy to tell the differences when they are side by side. • Because hairs vary on one person, you will need several samples from different parts of the body. • Human error is the biggest problem is matching samples. • Once a match is made, it has to be confirmed with DNA.

15. Factors in Comparison of Hair • It is fairly easy to tell which part of the body the hair came from. • Use length, medulla type and uniformity. • You can generally tell race from hair, but it is not 100%. • We cannot tell age from hair. • We can use DNA to figure out the sex. • If hair falls out, there is no root ball attached to use DNA.

16. Individualizing Human Hair • We can find nuclear DNA in the root or on a follicular tab. • The follicular tab is the best place to find nuclear DNA. • Getting hair roots for DNA is easier while the hair is in the growth phase. • Unfortunately, most hair at a crime scene is hair that fell out, not pulled.

17. Individualizing Human Hair • The exception is for violent crimes. • If hairs have fallen out, we can use mitochondrial DNA. • This is DNA that is passed from the mother to the child. • Nuclear DNA has parts from both mother and father. • Mitochondrial DNA is easier to use because there are more copies.

18. Individualizing Human Hair • This means you can use a 1-2cm length to get DNA. • But if people are related, you cannot use this type of DNA.

19. Collection and Preservation ofHair Evidence • If you have a suspect hair, you need standard/reference hairs for comparison. (Controls) • Get these from the victim and other people at the crime scene. • You have to know what part of the body the hair came from to get the right correct reference hairs.

20. Collection and Preservation ofHair Evidence • Hair from a crime scene usually comes from the head or pubic regions. • For the head, you need 50 reference samples • For the pubic regions, you need 25 reference samples. • You need the full length of hair for comparison. • Have to pull the hair or clip it at the scalp.

21. Forensic examination of Fibers • Just like hair, fiber is left behind at a crime scene. • It is especially important in cases that involve personal contact. • Homicide, assault, rape • Fibers can be left behind in a hit and run or in screens or glass during a break in. • Since we cannot connect fibers to one person. It is circumstantial evidence.

22. Types of Fibers • We used to use only natural fibers • Starting in 1920, we started creating manufactured fibers. • rayon, nylon, spandex, polyester, etc. • Fibers come from clothing, carpeting, drapes, wigs, artificial turf, etc Natural Fibers • Made entirely from animal and plant sources

23. Types of Fibers Animal fibers • Wool (sheep), mohair, cashmere (goats), fur fibers (mink, beaver, etc.) and others • We use the same procedures as with human hair when identifying animal fibers • We still need reference samples to compare with

24. Types of Fibers Plant fibers • The most common plant fiber is cotton • Since white cotton is used so much, it is hard to match to a person. • The combination of colors in cotton makes it a little easier. Manufactured fibers • Rayon was created in 1911 and Nylon in 1939

25. Types of Fibers • Originally they were created by regenerated fibers. • These were made from raw materials made from cotton or wood pulp • This is treated chemically, dissolved, and forced through holes in a spinning jet to make fibers. • Today they are made from synthetic fibers.

26. Types of Fibers • Polymers = long chains of molecules put together from smaller units. • 1939 – nylon created by accident • A glass rod was put in a beaker and pulled out a strand that hardened when it hit air. • Polymers are the basic chemical substance of all synthetic fibers • Polymers are also used to make plastic, paint, adhesives and synthetic rubber.

27. Types of Fibers • Matter is made of molecules • Molecule = elements put together to make a new substance • Ex) H20, C6H12O6 • Most molecules have less than 100 atoms in them. • Polymers have millions of atoms per molecule • These are called macromolecules

28. Types of Fibers • Polymers are made of chains of monomers • Since there are lots of different monomers, the number of combinations is almost unlimited • Nature also make polymers • Proteins for animal hairs are polymers • DNA is a polymer • Starch is a polymer – it is chains of sugars put together.

29. Identification and Comparisonof Manufactured Fibers • If you are lucky you can get a piece of torn fabric that you can match with another piece of fabric • Normally, you only get a strand or two • You look at it under a comparison microscope. • Looking for color and diameter • If these two things do not match, you stop doing tests.

30. Identification and Comparisonof Manufactured Fibers • Other things you look for are stripes within the fiber or pitting in the fiber so you can make it look shiny. • Since each manufacturer has its own colors, we can match a fiber to a specific manufacturer. • This can link a fiber to a house or car.

31. How We Analyze Fibers • Chemical composition • We can find its general type (nylon) • We can find a specific type (nylon 6) • Fibers can be separated into 24 different categories. • People in the textile industry have lots of tests to determine the class of the fiber • Need lots of fabrics to do these tests.

32. How We Analyze Fibers • Criminalists only get a fiber or two to work with. 2) Bifringence • Polarized light that passes through a fiber will spilt in two. • The fiber will bend the light (refraction) • Each type of fabric refracts the light differently • You can look at a single fiber without damaging it.

33. How We Analyze Fibers 3) Infrared absorption • Different fibers absorb different amounts of infrared light. • We can do this while looking at it under a microscope. • It will not damage the sample so other tests can be run.

34. Significance of Fiber Evidence • We cannot say that a single fiber came from a single source • Databases exist for carpeting, but that’s it. • New fabrics come onto the clothing market all the time, no database for clothing. • With the huge amounts of colors and fiber types, to make the evidence mean something we have to do lots of test.

35. Significance of Fiber Evidence • Color, size, shape, how it looks under a microscope, chemical composition, dye type and content. • Unless it is denim or white cotton, we should be able to match it. • The more different fibers you can connect to someone, the stronger the evidence is.

36. Collection and Preservation of Fiber Evidence • Because trace evidence has become so important, crime scene investigators have to do a better job of finding it. • It occurs at almost every crime • You really have to look for it. • Clothing is put in to paper bags, each in a separate bag. • This is so you do not get cross contamination

37. Collection and Preservation of Fiber Evidence • Carpets, rugs and bedding are folded so no fibers get out. • Car seats are covered completely with plastic • Knives are protected to preserve fiber evidence • Tape is used to pick fibers off of skin • If fibers are loose, they are put in paper, the paper is folded, and then put into another container.

38. Collection and Preservation of Fiber Evidence • Once it gets to the lab, it is a long and tedious process to get through all of the evidence. • The crime scene investigator can make this easier by only collecting pertinent trace evidence. • The better the investigator is, the fewer the samples, the quicker the tests can be run.