FORENSIC SCIENCE. Trace Evidence

Transcription

1 FORENSIC SCIENCE Trace Evidence 1

2 Introduction Trace Evidence--any small pieces of material, man-made or naturally occurring. Trace evidence (in the absence of DNA) is considered class evidence. As early as the 1879, Dr. Rudolph Virchow realized that hair could only be used to eliminate suspects, but was not likely to conclusively link anyone to a crime. The appearance of the victim s hair is not inconsistent with having come from the accused. Remember me? 2

3 Trace evidence: Class evidence Most common examples: Hair Fiber 3

4 Hair Human hair is one of the most frequently found pieces of evidence at the scene of a violent crime. It can provide a link between the criminal and the act (Locard s Principle). From hair one can determine: Human or animal Race Origin Manner in which hair was removed Treated hair Drugs ingested 4

5 DNA The hair shaft contains abundant mitochondrial DNA or mtdna--inherited only from our mothers. It can be typed by comparing relatives when nuclear DNA is not available. It is commonly thought that only the root contains nuclear DNA. However, in rare instances, some nucleated cells called corneocytes can also be extracted from the normally degraded hair shaft. 5

6 Hair Morphology The Study of Structure and Form Parts of the hair Shaft--part of the hair that sticks out of the skin Root--lies below the epidermis Follicle--structure from which the hair grows 6

7 Hair Growth Terminology Anagen--hair that is growing Catagen--hair at rest Telogen--hair that is dying Length mm per day or 1 centimeter per month; approximately one half inch per month 7

8 Hair Cuticle The cuticle is the outermost layer of hair which is covered with scales. Scales also always point toward the tip of the hair. 8

9 HUMAN SCALES In order to visualize the scales paint fingernail polish on a slide place a hair on the polish lift off the hair and observe the scale imprints What pattern is seen in this slide? 9

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11 Scale Types Imbricate 11

12 Scale Types Mosaic Chevron 12

13 Scale Types (cont) Pectinate 13

14 Scale Types (cont) Petal Diamond Petal 14

15 Hair Cortex The cortex gives the hair its shape. It has two major characteristics: Melanin--pigment granules that give hair its color Cortical fusi--air spaces, usually found near the root but may be found throughout the hair shaft 15

16 Hair Medulla The medulla is the hair core that is not always present. The medulla comes in different types and patterns. Types: Continuous Intermittent or interrupted Fragmented Absent--not present 16

17 Uniserial Multiserial Vacuolated Lattice Hair Medulla Patterns Amorphous (without a distinct pattern) 17

18 HUMAN MEDULLA Human medulla may be continuous, fragmented or absent. 18

19 RABBIT MEDULLA Rabbit medulla is different depending on the type (location on the rabbit) of hair. The one to the left is multiserial. The one to the right is a uniserial ladder and is found in guard hair. 19

20 Medullary Index Determined by measuring the diameter of the medulla and dividing it by the diameter of the hair. Medullary Index for human hair is generally less than 1/3. For animal hair, it is usually greater than ½. Cats medullary index ratio is very high-higher than dogs! Compare below-which side is cat and which is dog? 20

21 Hair Comparison Color Length Diameter Distribution, shape and color intensity of pigments granules Dyed hair has color in cuticle and cortex Bleaching removes pigment and gives yellow tint Scale types Presence or absence of medulla Medullary type Medullary pattern Medullary index 21

22 Collection of Hair Evidence Questioned hairs must be accompanied by an adequate number of control samples. from victim possible suspects others who may have deposited hair at the scene Control Sample 50 full-length hairs from all areas of scalp 24 full-length pubic hairs 22

23 Advantages: Hair Toxicology Easier to collect and store Is externally available Can provide information on the individual s history of drug use. Collections must be taken from different locations on the body to get an accurate timeline. 23

24 HAIR TESTING Procedure Collect an adequate sample, cut as closely to the scalp as possible. Wash the hair to remove lipids, oils, cosmetics and any drugs adhering to it Cut it into one centimeter sections Place hair in a digesting solution Screening test--antibodies are added to the hair that bind with the drugs. If this shows that drugs are present: A confirmation test is done by gas chromatograph 24 and then a mass spectrometer.