Some research on forensics (:

What exactly is Forensic Science?
Forensics science is basically the use of science to analyse evidence & clues left behind in a crime scene. This can help to determine many aspects of the crime committed, such as the murder weapon, characteristics of the culprit, etc. 


Fields of Forensic Science (taken from http://www.ehow.com/facts_5200426_different-fields-forensic-science_.html, http://www.mtholyoke.edu/org/forensic/fields.html)

• Ballistics
• Ballistics specialists are experts in firearms. They use shell casings, examination of exit and entrance wounds or holes in objects, firearms, and bullets to help investigators determine the type or location of a weapon that was used.
• Blood Spatter Analysis
• Blood spatter analysis experts use bloodstains and spatters that are left at a crime scene to answer questions to the type of weapon used, the location of the perpetrator and the victim, and the amount of force or number of weapon strikes.
• DNA Analysis
• DNA analysis is used to determine the identity of an individual using a sample of hair or bodily fluids, such as saliva, blood or semen.
• Trace Evidence Analysis
• Trace evidence is small bits of evidence such as fibers, hairs, dirt or grass that are deposited at the crime scene and can help lead identifiers to a perpetrator. 
• Anthropology
• Forensic anthropologists use their knowledge to identify human remains such as bones. They determine the age and sex of an individual based only on the skeleton or skull, and might also be able to theorize as to the cause of death or weapon used.
• Also studies human relationships (although this seems more like detective work?). Probably helps to determine who the culprit is, & what his motive is.
• Entomology
• The study of bugs. Probably only for corpses. When a corpse is left over a period of time (days, weeks, maybe even months?), the number & species of bugs inhabiting it changes accordingly. So with entomology, the specific time of crime could be estimated.
• Odontology
• The study of teeth. Teeth marks can tell some things about the perpetrator & the crime. Apparently, the teeth marks differ when the muscle of the victim is flexed or not (ie. the biceps). So it would show whether or not there was a struggle. (although there will probably be more clues already to show that?) It can also vaguely determine the race of the perpetrator. This science is not very evolved yet.
• Latent Print Identification
• Latent prints of footprints, handprints, fingerprints, etc. can help in determining the culprit.