ForensicsHair, Paint, and Fibers

•A. Morphology of hair–1. HAIR IS AN APPENDAGE OF THE SKIN THAT GROWS OUT OF AN ORGAN KNOWN AS A HAIR FOLLICLE.

•2. The length of hair extends from its root or bulb embedded in the follicle, continues into a shaft, and terminates at the tip end.

•3. The shaft is composed of three layers that forensic scientist are most interested in.–The cuticle, cortex, and medulla.

•4. The cuticle is the outer layer of the hair. It is composed of overlapping scales that always point toward the tip end of the hair. These scales make the hair resistant to decomposition and help it retain its structural features for long periods of time.

•Hair by itself cannot be identified to a single person but it can be used to identify animal species because of the differences in scales.

•5. The layer underneath the cuticle is the cortex. It is the main body of the hair shaft. Its most important forensic aspect is that it is embedded with pigment granules that give its color. This helps with comparison.

•6. Medulla is a cellular column running through the center of the hair. In some animals this column takes up a large part of the hairs diameter. This is known as the medullary index.

•In humans it is 1/3. The presence and appearance of the medulla varies greatly.

•Some have a continuous medulla.

•Some have interrupted medulla.

•Some have fragmented medulla.

•Most human head hair have no medulla. If present it is usually fragmented. Except the Mongolian race who have continuous medulla.

•There is a searchable database available which examines hair based on scale patterns and medulla type.

•7. Roots – the root and other surrounding cells contained within the hair follicle provide the tools necessary to produce hair and continue its growth.

•There are three phases of hair growth.

•Anagen – 1st phase, may last up to six years. The hair follicle is attached to the root. If the hair is pulled out with the root attached it will contain a follicular tag. These are important for doing DNA analysis.

•Catagen – 2nd phase. Hair continues to grow but at a slower rate. Lasts about 2 to 6 weeks.

•Telogen – the final stage. Hair growth has stopped. During a 2 – 6 week period the hair will be pushed out of the follicle and shed.

•8. Identification and comparison of hair–The crime lab will be asked to identify which species the hair came from or if the hair came from another individual involved in the crime.

•A comparison microscope is used for this task.

•They may be able to identify chemicals on the hair or when the hair was last dyed.

•Hair grows at an average of I cm per month. Other factors learned from examination include disease, infection, or drug use.

•9. Can the body area from which a hair originated be determined? Yes, by looking at pigmentation, courseness, diameter and tips.

•10. Can the racial origin of hair be determined?

•Usually

•African Caucasian

*Pigment is *Very fine to dense and coarse pigmentsunevenly distributed evenly

distributed

*Flat to oval *Oval cross-

cross-section section

•11. Can the age and sex of an individual be determined from hair?

•Age can only be determined for infants.

•The recovery of DNA can prove male or female origin.

•12. Is it possible to determine if a hair was forcibly removed from the body?

•A hair root that has follicular tissue adhering to it is indicative of a hair that has been pulled out. Hair that falls out naturally will have a root free of tissue. However, hair that is pulled out slowly is less likely to have root tissue that hair pulled out quickly.

•B. Fibers•1. Natural fibers are derived in whole from animal or plant sources. Animal fibers account for the majority of natural fibers encountered in the crime lab.

•These include hair coverings such as wool, mohair, cashmere, mink, etc. The procedure for analyzing these is basically the same as that for hair.

•The most common plant fiber is cotton. Unfortunately the wide use of this makes it hard to use as evidence.

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•2. Man-made fibers. These are fibers derived from either natural or synthetic polymers. The fibers are typically made by forcing the polymer material through the hole of a spinneret.

•Most of the fibers currently manufactured are produced solely from synthetic chemicals and are therefore classified as synthetic fibers. Examples include nylon, polyester, and acrylics.

•3. The polymer is the basic chemical substance of all synthetic fibers. Polymers are long-chained molecules. Examples of things manufactured from polymers are plastics, paints, adhesives, and rubber.

•4. The first step in analysis of a fiber is microscopic comparison for color, shape, and size using a comparison microscope.

•The second step would be to analyze the dye or dyes present on the fibers.

•The last phase of comparison is to determine if two fibers are chemically identical.

•C – Forensic Examination of Paint.

•1. One of the most commonly encountered types of physical evidence, most frequently in hit-and-run and burglary cases. Usually the forensic scientist will be asked to compare two or more paints for the purpose of determining common origin.

•2. The paint from an automobile can be used to determine the color, make, and model of a car.

•3. What is paint made of?

•Paint is composed of pigments (to give color and hiding quality) and a binder which provides the support medium for the pigment and other additives. The binder is usually a polymer.

•4. Automotive paint – there are four basic coatings for auto paint.–a. The ELECTROCOAT PRIMER is the first layer. It is electroplated onto the steel body to provide corrosion resistance. Usually grey or black in color.

–b. The PRIMER SURFACER is applied over the electrocoat primer. Its function is to smooth out and hide seams or imperfections.–Color differs.

–c. The BASECOAT is the layer that provides the color and appearance of the finish. Mica pigments, aluminum flakes, and other materials are added to give paint an individual and unique appearance.

–d. The CLEARCOAT has no color and is used to provide gloss and add durability.

•The microscope has traditionally been and remains the most important instrument for locating and comparing paint specimens.

•Color imparts paint with its most distinctive forensic characteristics.

•The importance of layer structure for evaluating the evidential significance of paint is very important.

•When paint specimens posses colored layers that match with respect to number and sequence of colors a common origin can is probable.

•The diverse chemical composition of paint can provide for additional points of comparison between specimens.

•A thorough comparison of paint must include a chemical analysis of either the paint’s pigment, binder, or both.

•Pyrolysis gas chromatography is a valuable and accepted technique for distinguishing most paint formulations. In this process paint chips as small as 20 micrograms are decomposed by heat into numerous gas products.

•These products are sent through a gas chromatograph. What emerges and is recorded are the separated decomposition products of the polymer used in the paint.

•It is the pattern of this chromatogen or “pyrogram” that distinguishes one polymer from another. What results is a pyrogram that is sufficiently detailed enough to reflect the chemical make-up of the binder.

•Infrared spectrophotometry is another analytical technique used to provide information about the binder composition of paint. Binders will selectively absorb infrared radiation to yield a spectrum that is highly characteristic of a paint specimen.

•The elements that comprise the inorganic pigments of paint can be identified by either emission spectroscopy, neutron activation analysis, X-ray diffraction, and X-ray spectroscopy. The emission spectrograph can simultaneously detect 15 to 20 elements in most automobile paint.

•Crime labs are often asked to identify the make and model of a car from a very small amount of paint left behind at a crime scene.

•Color charts for automobile finishes are available from paint manufacturers.

•Starting in 1974 the Law Enforcement Standards Laboratory has collected and given out to crime labs auto paint samples from domestic passenger cars.

•The data collected from crime scenes can be compared to data in the Paint Data Query Database to determine possible make, model and year of the paint.

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