1 Forensic Science Chapter 3: Physical evidence

2 Biologicals Blood, semen, and saliva.  Liquid or dried  Human or animal  on fabrics  Cigarette butts Serological and biochemical analysis  Identity  origin

3 Documents Handwriting and typewriting  Authenticity  Source Paper Ink Indented writings Obliterations Burned or charred

4 Drugs Any controlled substance Paraphernalia  Use  Manufacture  Sale

5 Explosives Charges Objects with residue

6 Fibers Natural or synthetic Transfer  Between objects  Between persons

7 Fingerprints Visible Latent  Not visible yet, but able to become so

8 Firearms and ammunition Discharged intact

9 Glass Particles or fragments  Transfer Windowpanes  Bullet or projectile holes

10 Hair Animal or human Transfer DNA Visual comparison

11 Impressions Tires Shoes Gloves Bite marks tracks

12 Organs and bodily fluids Toxicology Includes blood alcohol level

13 Paint Liquid or dried transfer

14 Petroleum products Arson Stains that suggest presence at the scene

15 Plastic bags Trace origin

16 Plastic, rubber, and other polymers Man-made transfer

17 Powder residues gunshots

18 Serial numbers Stolen property Can be recovered if filed off

19 Soil and minerals Link to location  Shoes  Carpet  tires

20 Tool marks Impressions Scrapes

21 Vehicle lights On or off at impact

22 Wood or other plant matter Transfer  Clothing  Shoes  Tools

23 Identification The process of determining a substance’s physical or chemical identity examples  Drug analysis  Species determination  Explosive residue analysis Must have a standard reference  Eliminate all other possibilities  Beyond reasonable doubt May require more than one test  Must do enough to exclude all other substances

24 Comparison The process of ascertaining whether two or more objects have a common origin Subjects a suspect and a standard/reference sample to the same tests and examination Involves probability – the frequency of occurrence of an event Examples  Hair  Paint chips Select properties  Distinguishable  Probability

25 Individual characteristics Properties of evidence that can be attributed to a common source with an extremely high degree of certainty. Examples  Fingerprint ridge characteristics  Striations or tool marks  Handwriting  Irregular wear patterns on tires or shoes

26 May not be possible to state probability mathematically, but it is high Must be substantiated by experience Example – mathematically determined that the probability of two people having the same fingerprints is 1 out of 1 x  In the past 100 years, no two fingerprints have been found that are exactly the same.

27 Class Characteristics Properties of evidence that can only be associated with a group and never with a single source Example – paint  If there is only one layer, you can narrow it down to at best one car model  If there are seven layer and they are all the same, you can narrow it down much more

28 Example – blood  26% of the population has type A blood  Other factors can be used to narrow it down further

29 Product Rule Multiplying together the frequencies of independently occurring genetic markers to obtain an overall frequency of occurrence for a genetic profile.

30 Example – O.J x 0.85 x 0.02 = or 0.44% 0.44% of the population has blood like this, or 1 out of every 200 people. Blood FactorsFrequency A26% EsD 185% PGM 2+2-2%

31 Disappointment A fiber, hair, or paint chip often cannot be matched to one specific source. Usually need a lot of possible matches to get one probable match. Also used to corroborate witness testimony or confessions.

32 Example Case study – 28 different fibers linked Williams to murder victims More than just coincidental

33 Exoneration Class evidence may exclude suspects Example  If type A blood is found at the scene, suspects with types B, O, and AB blood are excluded

34 How much is enough? No simple answer Get as much as you can

35 Reconstruction The method used to support a likely sequence of events by the observation and evaluation of physical evidence, as well as statements made by those involved with the incident. What happened before, during, and after the crime? Requires cooperation of medical examiners, law enforcement, and criminalists

36 Examples Determining the path of a bullet with a laser Was the body moved after death? Blood-spatter analysis to find direction of impact Using gunshot residue to determine distance from shooter