The biology section detects and identifies biological material on exhibits collected from a crime scene such as clothing, weapons or personal effects.
Evidence from a crime may link a suspect or victim to a crime scene or another person. Swabs taken by police at crime scenes or exhibits submitted to Forensic Science SA (FSSA) are swabbed by evidence recovery technicians to obtain DNA profiles.
DNA (deoxyribonucleic acid) is a chemical that is present in almost all cells. This chemical is not only responsible for biochemical processes in the body but also determines our physical attributes. It is the genetic information that is carried down from parents to a child. Half of the information is obtained from the mother, the other half from the father. DNA molecules are very complex and contain a lot of information.
For forensic purposes only a small number of locations on the DNA are investigated, which can vary greatly in length between different people. These locations do not contain any information about appearance or other physical attributes. DNA profiles can be used to distinguish between individuals, match individuals to crime scene samples or reveal the identity of a deceased person who cannot be visually identified.
Video: working in forensic biology
Swabs are mostly processed using a robotic system, as it is a highly repetitive process that can be automated. In this process, DNA is removed from the cell, quantified and small amounts of DNA amplified using a method termed PCR (polymerase chain reaction). This technique can be likened to a molecular photocopy machine – it allows an increase in amount of the material of interest.
If a criminal suspect has been identified by the police and a reference sample for that person submitted to FSSA, their DNA profile can be compared to crime scene samples.
If the suspect of a crime is unknown (often the case in ‘volume crime’ such as breaking and entering, and theft), then the profile obtained is uploaded to a local and national DNA database and searched against other profiles on the database. This often leads to a match with a reference sample, providing an investigative lead for police to follow. Many suspects for volume crime and old unsolved “cold cases” particularly sexual assaults are identified in this way.
The evidence recovery section documents, examines and recovers biological and physical evidence from exhibits collected from crime scenes or persons of interest. These exhibits can include weapons, clothing, bedding and personal effects. Documenting evidence is important for chain of custody and to be able to accurately and factually present that evidence to the court. Evidence examiners use specialised enhancement techniques to locate traces of blood, saliva and other body fluids on these exhibits. When biological evidence is located, samples are recovered for DNA profiling. Other forms of evidence recovered may include drug residues or glass fragments (see chemistry).
Evidence examiners are also trained in the analysis and interpretation of bloodstain patterns on clothing and weapons. While DNA profiling can tell us who was involved in a crime, bloodstain pattern analysis can tell us what happened. This evidence can confirm or refute witness statements relating to the events that occurred at a crime scene. Evidence examiners also interpret damage to textiles, such as clothing, to determine if the damage was recent, cut or torn and if a particular weapon has been used to create that damage.