fo-ren-sic: involving the application of scientific knowledge to legal matters.

—Webster's New World Dictionary

Physical Evidence

Physical evidence is any evidence that is left after criminal activity has taken place. It is a good example of Locard's principle of exchange. This is a more general field that relates to other more specialised branches of forensic science, such as ballistics and fingerprints analysis.

Imprints and compressions:

footwear patterns
tyres
tool marks and scratches
bites

Tool mark identification uses similar techniques to ballistic identification procedures, such as the forensic macroscope. Not only can tools leave tell-tale scratches on the materials they come in contact with, they may also deposit paint and metal particles. For bites, dental records may be used.

Trace materials:

paints and other deposits
hair and other fibres
pollens
glass and polymers

... in fact all substances that are identifiable and traceable to geographic areas, persons, manufacturers etc.

Chemical analysis may be performed on microgram quantities of materials which the criminal doesn't know are there, but they are incriminating evidence.

Activity

Now print out the worksheet for this topic and visit these web resources to get your information.

Impressions and tracks:

Sign cutters (trackers) are people who can read signs of the progress of a journey through all kinds of country

Try this track quiz and test your observation skills!

C.A.S.T. Website (Chesapeake Area Shoeprint and Tyre track)

Look at the instructions sections found under both footwear and tyre track headings.

Hairs:

Hair shape and structure (called morphology) is genetically determined. Hairs have particular diameters, colours, kink patterns etc.

From a single strand of hair we can learn:

the race of the person or the species of animal
what part of the body it came from
whether it was pulled or had fallen out
any association with insects such as hair lice
a person's state of health. Levels of toxins, drugs and vitamins are all reflected in the hair

Go to the hair fibre picture gallery (this site is very new and may not be yet fully available).