Today, more than ever, the quality of evidence in criminal cases is scrutinized in the courtroom. Both defense and prosecuting attorneys look to the manner in which evidence is collected and handled to bolster their cases.

Many trials involve highly technical testimony about the chemistry and biology of evidence and the physics of how it was analyzed. But all that science can easily be thrown out when the method of actually collecting the evidence is in question. It’s up to those law enforcement and forensic specialists at the crime scene to ensure that all the I’s are dotted and the T’s are crossed when it comes to the evidence. The goal should always be to eliminate questions before they become an issue; aim to never lose a case on a technicality. On cases that go to court, any unexplained evidence collected at the scene needs to be identified. Unidentified evidence such as latent fingerprints, shoe tracks, hair, blood, and DNA swabbing will need to be identified. If not identified the question is: Could it be from the actual suspect who committed the crime?

One place crime scene investigators can look to make certain that evidence is of the highest quality is contamination. Contamination is the introduction of something to a scene that was not previously there. Most contamination at a crime scene comes from the humans who investigate it. There are several ways that a crime scene and what is gathered there can become contaminated but a little common sense can alleviate the problem

Evaluating a scene before anyone enters can be key to keeping contamination to a minimum. Careful appraisal can lead to an overall plan as to what needs to be collected and the best means to collect it. This can help decrease the threat of contamination. When doing a preliminary survey of the crime scene to evaluate it as to equipment and manpower needs, be aware of your limits. Some scenes may require the presence of a specialist such as a serologist, blood spatter expert, or latent people to name a few. They may be from other agencies in the area or the local crime lab. Some of the evidence at the scene may need to be evaluated prior to collection. A particular case I assisted with had a large amount of blood and blood spatter at the scene (this was prior to DNA). Three serologists were brought to the scene from the local crime lab and approximately 200 samples were charted and collected. Laboratory examination revealed that several samples collected were not the victim’s blood instead it showed that the suspect had been cut.