Science of Crime Scenes Chapter 6.2 Science of Crime Scenes

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

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

Science of Crime Scenes DNA The quantity of DNA present in each cell is about 6 picograms 6.10-12 g 0.6 ng (6.10-10 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

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

DNA collection on non-porous surface Science of Crime Scenes

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

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

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

Blood detected by Bluestar on fence Science of Crime Scenes

Bloody shoeprint developed with Bluestar Science of Crime Scenes

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

Science of Crime Scenes

Science of Crime Scenes

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

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