1. Science of Crime Scenes
Chapter 6.2
Science of Crime Scenes

2. Science of Crime Scenes
Biological Evidence
Distinction between body fluids and tissues and DNA
Biological materials: Blood, hair, semen, saliva, etc.
Molecular information: DNA
Biological materials are also useful for toxicological examinations
Science of Crime Scenes

3. Science of Crime Scenes
DNA
Dexoxyribonucleic acid (DNA) is a molecule present in every living cell
encodes the information needed for the development and the life cycle of organisms
DNA appears as a double helix of about 6 billion paired nucleotides
Each made of a phosphate associated with a sugar on which is linked one of the following four bases:
Guanine (G)
Cytosine (C)
Thymine (T)
Adenine (A)
Bases constitute the links between the two sides of the helix chain
Adenine only bonds to Thymine
Cytosine only bonds to Guanine
Science of Crime Scenes

4. Science of Crime Scenes
DNA
The quantity of DNA present in each cell is about 6 picograms g
0.6 ng ( g) produces a DNA profile of good quality
Which means that only about 100 cells are required
Even if such a small quantity of DNA is collected and later profiled, what does it mean to have found so low an amount of material?
Science of Crime Scenes

5. Science of Crime Scenes
Collection
Porous materials are easy; the cells are trapped in the material
Non-porous materials are more difficult; recommended protocol:
Photograph any perishable pieces of information that may be destroyed by swabbing
Using a sterile cotton swab that has been soaked with distilled water and from which excess water has been removed, swab the surface aggressively
Document details regarding the exhibit description and area(s) swabbed.
Air-dry in a cabinet to prevent contamination
Once dried, transfer the swab into a DNA tube for processing
Science of Crime Scenes

6. DNA collection on non-porous surface
Science of Crime Scenes

7. Science of Crime Scenes
Blood
A human being has about 5 liters of blood
Blood is a matrix of free cells (red, white globules) and anticoagulant platelets carried by the plasma (the liquid portion)
Plasma is about 55% water
Red blood cells (erythrocytes) compose 99% of the solid elements of blood
Not really “cells,” as they do not possess a nucleus
Carry oxygen through hemoglobin, which uses iron to bond the oxygen
The iron is targeted for presumptive tests for blood
Science of Crime Scenes

8. Where does the DNA come from?
White cells (leukocytes) and platelets compose approximately 0.3% and 0.7% of the solid elements of blood
The former are dedicated to combating infectious agents
Leukocytes are the only ones containing DNA
Science of Crime Scenes

9. Science of Crime Scenes
Detection of blood
Bluestar® forensic reagent, based on Luminol, is presently the most efficient commercial product for visualization of suspected blood at the crime scene
Easily sprayed, it can also be used for spot tests with cotton swabs
Science of Crime Scenes

10. Blood detected by Bluestar on fence
Science of Crime Scenes

11. Bloody shoeprint developed with Bluestar
Science of Crime Scenes

12. Science of Crime Scenes
Spatter patterns
Can be illustrative of the points of origin and determining where they intercept a target surface
The direction of travel can be determined by the direction of the greatest edge distortion
SAADD
A: Alignment of individual spatters with respect to the whole pattern
A: Alignment of individual spatter stains with respect to each other
D: Distribution (density) of the number of spatters
D: Distribution (frequency) of spatter size ranges
Science of Crime Scenes

13. Science of Crime Scenes

14. Science of Crime Scenes

15. Science of Crime Scenes
Semen
Semen is a mixture of various fluids that carry live spermatozoa to the female ovule for fertilization
A fertile semen sample holds tens of millions of spermatozoa per milliliter
Various spermatozoa nutrients are immersed in the seminal fluid
Proteins (vitamins and phosphatase)
Mineral salts
Testosterone
Provides useful DNA evidence, due to the DNA contained in the spermatozoa head
Science of Crime Scenes

16. Duration for collection
Viable semen for forensic analysis can found:
19 days in the cervix
10 days in the vagina
110 hours in the rectum
44 hours in the anus
31 hours in the mouth
The presence of spematozoa is conclusive for sexual contact
Science of Crime Scenes