no diatoms, it can be concluded that thedrowning took place in a bathtub or sink since diatoms are filtered from tapwater. A scanning electron microscope that can magnify objects 100,000times is used to detect tiny gunpowder particles present on he hand of aperson who recently fired a gun. One of the oldest techniques of forensic science is dusting the scene ofa crime for fingerprints. In one method of obtaining a fingerprint, a technicianspreads fine powder over a surface with a brush or magnetic wand. Thepowder sticks o proteins secreted by the sweat glands on the skin ridges ofthe fingertip When the excess powder is removed, an outline of the contoursof the ridges remains. The print may also be chemically treated to reveal thecontours. Since no two fingerprints are the same, fingerprinting is a positiveway of identifying someone.Other evidence that may be found at a crime scene is blood, hair, skin,or semen. Human bite marks can also serve as evidence. Bites can be foundon the victims body or in pieces of food or gum found at the crime scene. Aforensic scientist can fill the impression caused by the bite marks with a liquidplastic. The cast will form an accurate replica of the assailants teeth which isthen compared with a cast of the suspects teeth. District attorneys call forensic scientists to give their expert testimonyin a trial concerning what they find from an autopsy and what they write inthe lab reports. Expert testimony is the statement given by a specialist whohas been recognized as having expert knowledge about evidence in the case.An expert witness is allowed to give an opinion about whether or not theevidence is valid. An expert witness may also quote the statements of otherexperts to support an opinion. Ordinary witnesses are restricted to givingstatements about what they actually saw or heard.The medical and legal approach to dealing with crimes began inEngland during the 12th century. King Richard I establi...
