What is Forensic Science?

Forensic science is any science used for the purposes of the law, and therefore provides impartial scientific evidence for use in the courts of law, eg in a criminal investigation and trial. Forensic science is a multidisciplinary subject, drawing principally from chemistry and biology, but also from physics, geology, psychology, social science, etc.

In a typical criminal investigation crime-scene investigators, sometimes known as scene-of-crime officers, will gather material evidence from the crime scene, victim and/or suspect. Forensic scientists will examine these materials to provide scientific evidence to assist in the investigation and court proceedings, and thus work closely with the police. Senior forensic scientists, who usually specialise in one or more of the key forensic disciplines, may be required to attend crime scenes or give evidence in court as impartial expert witnesses.

Examples of forensic science include the use of gas chromatography to identify seized drugs, DNA profiling to help identify a murder suspect from a bloodstain found at the crime scene, and laser Raman spectroscopy to identify microscopic paint fragments. While the procedures of forensic science can be useful in solving a crime, it is important to remember the role of forensic science in the overall process of finding the guilty suspect.

There may be many suspects in a criminal investigation. To find the guilty suspect, an investigator must ensure that the following three criteria have been met:

MotiveReason(s) why the crime was committed. Some possible motives are passion, jealousy, greed and revenge. Motive is usually determined through interviews and research

OpportunityBeing able to place the suspect at the scene of the crime, or in a position to be able to commit the crime

MeansBeing able to establish through evidence that the suspect was able to commit the crime.

To assist the investigator in finding the suspect that meets all three of the above criteria, the forensic investigator has an important role (in some instances, the investigator and the forensic investigator may be the same person). It is important that at a crime scene every effort is made to secure the site so that evidence is not destroyed or altered. The investigator(s) could take photographs and collect fingerprints and samples such as hair, fibres, blood, soil and/or foreign objects from the crime scene and suspects.

The job of the forensic investigator will be to use science and technology to perform tests on the evidence collected. The results from these tests can then be used in support of an investigators theory of who is the guilty suspect.

There are many different disciplines or areas that forensic scientists specialise in -- these include ;

- Fingerprinting

Pattern of tiny ridges on the outer layer of the skin on our fingertips which are unique, and used for identification.

- Fibres and Hair samples

Hair and fibres are amongst the most common items left as trace evidence at a crime scene and they can provide vital information for forensic scientists.

- Firearms and tool mark identification

Firearms and tool mark identification involves more than just guns. Also included in this broad subject area are explosives, imprint evidence and tool mark evidence. A typical firearms examination concerns matching a bullet back to the gun that fired it, to the exclusion of all others.

- Ballistics and bullet matching

Certain parts of a firearm mark the bullet and cartridge. Rifling gives the bullet a signature marking that is unique to the weapon that fired it. Rifling exists as part of the manufacturing process of the firearm and serves to put spin on the bullet, giving it a straighter trajectory (much the same way a quarterback puts spin on a football.

- Footprints and tyre prints.

There are two basic types of imprint evidence: Three dimensional impressions, in which an object presses into something soft which retains the impression of that object; and two dimensional impressions, in which an object transfers an image to a surface or an object comes into contact with a surface that is coated and removes some of that coating.

- Explosives.

Without getting too into it, explosives residue can be analyzed to determine the type of explosive used in a particular detonation

- Entomology.

To paraphrase Indiana Jones, "Bugs. I hate bugs..." But they are great evidence and can be used to determine time of death. In some cases, they can be used to determine if a body has been moved from one geographic location to another. Certain bugs incubate and hatch at certain known rates. If bugs are found on a corpse, the age of the bugs can be extrapolated backward to estimate time of death.

- Blood Spatters.

Blood spatters help a great deal in reconstructing a crime scene. They can be used to corroborate or disprove and alibi. They can be used to convict the guilty.

- Paint chips

Paint can be examined and matched for colour and texture. Also, a paint chip can be fracture matched back to the point from which it originated

- Rope, Twine, Cord.

In the event of death by hanging, skin tissue on the fixed side of the rope can indicate homicide rather than suicide. Never cut a noose or alter the knot. There is the possibility of a fracture match if the length of rope found at the scene was cut from a larger length of rope. - Blood Spatters.

Blood spatters help a great deal in reconstructing a crime scene. They can be used to corroborate or disprove and alibi. They can be used to convict the guilty.

- Soil.

Soil can be used to associate a particular scene with a particular individual. Typical collection sites include shoes, tires, pedals, carpeting and wheel wells on cars. Soil can also be used to determine if an individual has been moved

-Glass.

Class characteristics of glass include its colour, thickness and refractive index (how much it bends the light that passes through it), and whether it is flat or curved. Individual characteristics include fingerprints, fracture matches, saliva or lip prints (if it is a drinking glass or someone has pressed their face against a window), blood and prints from nose, tongue, chin or mouth. There may be a drug or liquid residue on the glass or even footprints if the glass if found on the floor.