Police Rules for Collecting Evidence

Written by yvonne van damme
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Police Rules for Collecting Evidence
Fingerprints are a common type of evidence that police collect and process. (Hi Detail Fingerprint 2 image by Andrew Brown from Fotolia.com)

One of the primary duties of police officers, detectives and crime scene processors is to obtain, preserve and properly package evidence from the scene. This involves expertise, the correct tools and true diligence. Since evidence at crime scenes can be easily destroyed or ruined, police officers must take care when handling it. Also, if it isn't handled properly while in transit or when it reaches the laboratory, the evidence could be ruined and the case never solved.


There are certain rules for collecting firearms, bullets and residue from a crime scene. First of all, when you find a firearm, you must remove the magazine. However, do not take the actual gun apart. Don't submit a loaded gun to a crime laboratory. Also, don't ever clean any part of the gun, the cylinder, chamber or bore. To do so is to ruin any evidence on the gun. While collecting this evidence, record the make, model, calibre and serial number of the gun.


The lifting and preservation of fingerprints is extremely important. As prints are delicate and easily destroyed, the police officer must take great care in obtaining them and keeping them from smudging. While picking up exhibits or items, using a clean cloth or wearing latex gloves is essential. If using cloth, you must take extreme care not to wipe or smear prints, as it can happen easier than with gloves. In all cases, every precaution must be taken to not destroy the fingerprints on the scene or add fingerprints to the scene. When handling documents or papers that contain fingerprints, they should be individually placed in cellophane. The cellophane can then be placed between two sheets of cardboard.

Sexual Assault

There are specific rules for processing a crime scene with bodily fluids, especially those dealing with sexual assault. For all sex offences, a physician must examine the victim as soon as possible. The doctor will use a sexual assault collection kit to obtain fluids and fibres. In a sexual assault, blood and seminal stains can sometimes be found on sheets or clothing. Let the fluids air dry and then package the evidence in paper bags. Make certain to label each clothing item accordingly.

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