In examining biological evidence at a crime scene, the focus is on the identification and individualization of human tissues (Forensic, 2005, 227). This includes the analysis of blood, semen, saliva, feces, hair and abortion products. The first method employed to analyze DNA from crime scenes was restriction fragment length polymorphism (RFLP), which uses a restriction enzyme to cut DNA into smaller fragments separated by size using gel electrophoresis, transferred from the gel to a solid membrane, exposed to labeled DNA fragment probes, then exposed to a film and the final image is known as an autoradiograph. This test had many disadvantages, including needing sufficient sample for analysis, and has since been replaced by the PCR test, in which short tandem repeats are amplified to sufficient numbers for more accurate analysis then visualized in the same way, though the process is now fully automated so that a full genetic profile of a DNA sample can be matched to a known sample from a particular individual and this method is now widely accepted as evidence that the DNA came from a particular donor.
Forensic laboratories analyze physical evidence and use quality assurance programs designed to ensure the reported results are scientifically valid and the opinions are based only on the results that are considered reliable (Class, 2005). Trace evidence includes such evidence as fibers, hairs, body fluids, paint, glass, soil, and plant debris (Forensic, 2005, 228). Specimens are collected by hand picking, vacuuming, tape lifting etc. Fingerprint evidence is also collected by physical and chemical methods. There are three types of fingerprint evidence: a patent fingerprint is one that is visible and needs no processing; a plastic print is an indentation print which is recognizable and is left in some soft surface such as putty or tar; a latent print is one that needs additional processing to become visible (Forensic, 2005, 349)...