Biology

What is Forensic Biology?

Forensic biology is applied in any cases where the analysis of biological material may aid an investigation, for example crimes such as murder or rape.  The main biological materials of interest are blood, semen, other body fluids (such as saliva), hairs and fibres. 

It is useful to read about DNA as this is also a form of biological analysis. A DNA sample can be taken from most biological material and a DNA profile produced.  DNA profiling is a tool used by biologists to assist in the interpretation of scientific evidence.  A person's DNA profile can be compared against that of any recovered biological material to determine whether an individual may have been present at a crime scene.   

Blood and Blood Pattern Analysis

Blood can be compared to those involved in an investigation by DNA profiling. However it is also possible to examine the distribution of blood on an item and the characteristic patterns it forms (known as blood pattern analysis). This analysis can determine what actions took place to cause the blood to be transferred from one individual to another, such as punching or kicking.

For example, a blood stained jacket may be found in an accused's possession.  A forensic biologist may be able to determine whether the blood on the jacket was deposited as a result of the suspect having helped the bleeding complainer after being assaulted by someone else (the defence's position), or because the suspect repeatedly punched the complainer (the prosecution's position).

Damage Analysis

This involves the examination of clothing, footwear and other items for the presence of damage produced as a consequence of a criminal act.  Items are examined and information is provided by the expert as to the action causing the damage, for example - cut, slash, tearing etc. The forensic scientist is also able to give an opinion as to the age of the damage noted - recent or old - or as a result of wear and tear.
In some cases, the scientist will be able to provide information on what instrument caused the damage such as a single edged knife, a pair of scissors or a piece of broken glass.

Hair

The transfer of human hairs may take place in a wide variety of cases.  Commonly such cases involve the transfer of head hairs to hats or balaclavas or the transfer of head or body hairs to clothing and bedding (for example in sexual assaults), or the transfer of cut or broken hair fragments to an object (for instance on a weapon used to strike a victim, or even on a windscreen of a vehicle involved in a collision). Occasionally single head hairs may be found at the point of entry in housebreakings or clumps of hair pulled from a victim of a physical assault can be found on clothing or at the scene.

Textile Fibre Analysis

In cases where physical contact is an evidential issue for instance the accused is a stranger to the victim and is denying that any contact took place, or is denying that an alleged incident took place at a particular location (for example a bedroom), providing evidence of textile fibre transfer between the accused's clothing and the victim's clothing, or between the accused's clothing and fabrics such as bedding from a scene, may significantly aid an investigation.
In any case involving physical contact between people or objects, textile fibre evidence, based on Locard's Principle (every contact leaves a trace), may be significant.  However, fibre transfer examinations can be very time consuming and therefore before starting an examination the scientist will contact the submitting officer and may require them to complete a questionnaire to seek assurance that there has been no legitimate contact between an accused and the victim and that there has been no accidental cross-contamination prior to the items being received at the laboratory.

Case Study

A robbery was carried out at a pub in the West End of Edinburgh. As one of the robbers was leaving he spat on the pavement outside the pub.  Saliva was recovered and a DNA profile obtained.  The two robbers escaped in a stolen vehicle which was subsequently recovered. When the owner came to collect his car he complained about all the tissues on the floor of the car.  The second robber had a cold and discarded his used tissues in the car.  A DNA profile was obtained from the nasal secretions on the tissues.

Two suspects were later arrested and DNA samples taken from each.  These matched the profiles obtained from the saliva and nasal secretions and the two robbers were successfully prosecuted.