Real-life police evidence procedures bear little resemblance to those shown on the network crime shows. Because so many criminal cases depend on the validity of evidence, police procedures regarding the collection and storing of evidence are very strict.
Without proper police procedure in handling evidence, many criminal cases wouldn't have a leg to stand on. If a police officer came upon a scene covered in fingerprint evidence but didn't collect the evidence properly, the fingerprint evidence--though pointing directly to the person in custody--wouldn't be admissible in court.
Evidence collection has come a long way since the early days of American criminal justice. When eyewitness reports and speculation were the only tools police had, evidence collection was more an afterthought than a practice. Imagine how many people got away with their crimes before there were fingerprint databases and evidence-collection procedures. Today, evidence collection is the most important part of any conviction, other than an outright confession.
When a police officer comes upon a crime scene, he is instructed to not touch anything; this includes corpses, light switches, and any surfaces or objects. Most of the time evidence collection from the scene is performed by trained forensics teams. In some cases, the officer will collect any pertinent evidence. The first step after finding the evidence is proper collection procedures.
According to the California Law Enforcement Commission, "It is recommended that property/evidence be properly packaged and/or labelled to ensure its integrity and to protect against contamination, loss or theft. Proper packaging also protects employee health and safety. A sound packaging procedure helps to preserve the chain of custody, provides uniformity within the property room, and enhances the efficiency of the operation."
Today's criminal justice system is ever advancing in areas of evidence testing, collecting, storage and identification. There are several technological companies that specialise in designing, manufacturing and maintaining forensics equipment, and many advancements are being made. A decade ago it was impossible to distinguish one chemical trace from another, but in 2009 machines can test for specific chemicals, and where the chemicals were made.
Without police evidence procedures, many cases in the criminal justice system wouldn't stand a chance of conviction. Prosecutors or defence attorneys would have all the ammunition they needed to throw that case out due to inappropriate evidence collection or handling methods. With statewide procedures, the police and forensics professionals can collect and store evidence with the confidence that they've done their jobs right, and that they will get the bad guy in the end.