How evidence is collected from a scene of crime

Fingerprinting

The traditional method of finding fingerprints is to first brush all the surfaces where prints are likely to be found with fine aluminum power (black powder is used on pale surfaces). The powder is trapped by the lines of sticky, oily sweat left behind by the fingers on door handles, windows, drawers and furniture.

 These are photographed or taken away to the laboratory by sticking cleat adhesive tape over them. Then the tape is peeled away to reveal the powder pattern stuck to it. Sometimes the tape is stuck on cardboard for closer examination.

 If the pattern of fingerprints matches that of the suspect, it is likely that he or she was present at the scene of the crime.

 Fibers

The presence of a suspect on the scene of crime can be verified from fibers collected from the clothes worn by the suspect at the time crime was committed.

 Strips of sticky tape are pressed all over these clothes. If there are any loose fibers on these, they stick to the tape. The fibers are then examined under a microscope. Fibers not belonging to the clothes themselves may have come from the scene of crime-from the clothes of the victim, the carpet or the scene of crime. Chemical analysis is done to match them.

 Another technique used in comparing fibers is spectro-photometry. White light is shone through fibers that have been collected and this is split into a spectrum of colors by a spectroscope. Since fibers absorb different wavelengths of the light depending upon the dye present in them, different types of fibers produce different spectra. If the suspect’s clothes have fibers that match with the ones found on the scene of crime, then it can be proved beyond doubt that he/she must have been present on the scene of crime.