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Trace Evidence

Trace EvidenceHair and Fiber SamplesTrace EvidenceTrace evidence is circumstantial evidenceIt will not point to just one personIt can show a certain person was in a certain place.People have been found guilty just on circumstantial evidence.Forensic Examination of HairHair falls from the body every dayUnless 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.

Morphology of HairHair is made from skin cellsHair has 3 parts the cuticle, the cortex, and the medullaCuticleHair resists decompositionCorpses have been dug up with full heads of hair.It retains its structure for a long time.

Morphology of HairCuticle = 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.

Morphology of Hair3 basic patterns to cuticlesCoronal, spinous, and imbricate (page 413)We use these when matching samplesLooking at the scale pattern tells us if it is human or animal.2) CortexThis is the main body of the shaft.Looks like blocks stacked end to end.Morphology of HairThis is where the pigments for color are found.How the pigments are shaped and distributed gives us points for comparison.3) MedullaIt is a collection of cells running up the center of the hair.In animals, it makes up the width of the hair.For humans, it is generally 1/3 or less.

Morphology of HairThis 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.

Morphology of HairA cats medulla looks like a string of pearls. (page 416)There is a database of the 35 most commonly encountered animals.3) The rootRoot contains what is needed for hair to grow.The initial growth phase lasts 6 yearsWhen it is pulled from the root, it will have a follicular tagMorphology of HairWe use the tag for DNA samplesOnce the root stops growing, it shrinks.The hair will last 2-6 months before it falls out.

Identification and Comparison of HairIt tells us if it is animal or humanWill it match the suspect or victimWe will get samples from the scalp or pubic regions for comparison.Factors in Comparison of HairComparing human hairs has to be done carefullyWe 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 cuticleIt actually looks like another layer outside of the cuticle.

Factors in Comparison of HairBleaching 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. Factors in Comparison of HairIt 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.Factors in Comparison of HairIt 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.Individualizing Human HairWe 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.

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

Collection and Preservation ofHair EvidenceIf 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.

Collection and Preservation ofHair EvidenceHair from a crime scene usually comes from the head or pubic regions.For the head, you need 50 reference samplesFor 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.Forensic examination of FibersJust like hair, fiber is left behind at a crime scene.It is especially important in cases that involve personal contact.Homicide, assault, rapeFibers 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.Types of FibersWe used to use only natural fibersStarting in 1920, we started creating manufactured fibers.rayon, nylon, spandex, polyester, etc.Fibers come from clothing, carpeting, drapes, wigs, artificial turf, etcNatural FibersMade entirely from animal and plant sources

Types of FibersAnimal fibersWool (sheep), mohair, cashmere (goats), fur fibers (mink, beaver, etc.) and othersWe use the same procedures as with human hair when identifying animal fibersWe still need reference samples to compare with

Types of FibersPlant fibersThe most common plant fiber is cottonSince 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 fibersRayon was created in 1911 and Nylon in 1939 Types of FibersOriginally they were created by regenerated fibers.These were made from raw materials made from cotton or wood pulpThis is treated chemically, dissolved, and forced through holes in a spinning jet to make fibers.Today they are made from synthetic fibers. Types of FibersPolymers = long chains of molecules put together from smaller units.1939 nylon created by accidentA 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 fibersPolymers are also used to make plastic, paint, adhesives and synthetic rubber.Types of FibersMatter is made of moleculesMolecule = elements put together to make a new substanceEx) H20, C6H12O6 Most molecules have less than 100 atoms in them.Polymers have millions of atoms per moleculeThese are called macromolecules

Types of FibersPolymers are made of chains of monomersSince there are lots of different monomers, the number of combinations is almost unlimitedNature also make polymersProteins for animal hairs are polymersDNA is a polymerStarch is a polymer it is chains of sugars put together.Identification and Comparisonof Manufactured FibersIf you are lucky you can get a piece of torn fabric that you can match with another piece of fabricNormally, you only get a strand or twoYou look at it under a comparison microscope.Looking for color and diameterIf these two things do not match, you stop doing tests.

Identification and Comparisonof Manufactured FibersOther 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.How We Analyze FibersChemical compositionWe 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 fiberNeed lots of fabrics to do these tests.

How We Analyze FibersCriminalists only get a fiber or two to work with.2) BifringencePolarized light that passes through a fiber will spilt in two.The fiber will bend the light (refraction)Each type of fabric refracts the light differentlyYou can look at a single fiber without damaging it.How We Analyze Fibers3) Infrared absorptionDifferent 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.Significance of Fiber EvidenceWe cannot say that a single fiber came from a single sourceDatabases exist for carpeting, but thats 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.

Significance of Fiber EvidenceColor, 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.

Collection and Preservation of Fiber EvidenceBecause trace evidence has become so important, crime scene investigators have to do a better job of finding it.It occurs at almost every crimeYou 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

Collection and Preservation of Fiber EvidenceCarpets, rugs and bedding are folded so no fibers get out.Car seats are covered completely with plasticKnives are protected to preserve fiber evidenceTape is used to pick fibers off of skinIf fibers are loose, they are put in paper, the paper is folded, and then put into another container.Collection and Preserv

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