Movies, TV and novels tell us a great deal about forensic science. Some of what we see, hear and read offers excellent coverage of the topic—but some of it does not. Fictional TV shows and many movies offer just that—fiction. They are crafted with the goal of entertaining the public and not necessarily educating them. The problem is a universal one; if the storyline gets bogged down with factual information, the viewer or reader quickly loses interest.
The topic covered in this post deals with pollution of the crime scene. Not much film footage is devoted to this problem in the entertainment media. But it is indeed a big problem and if it isn’t dealt with in an intelligent manner, the available physical evidence in the scene may be damaged, compromised or destroyed altogether.
Many forms of physical evidence are highly fragile like fibers, hairs, blood droplets, DNA and fingerprints. Quite often the crime scenes and the evidence they contain are susceptible to various forms of chemical pollution too. The most common forms of chemical pollution are:
• Rain water and snow melt
• Seawater or water from rivers and streams
• Dust, dirt, oil and grease tracked in by the building occupants as well as the crime scene team
• Industrial and household chemicals
Contamination that arises from natural sources is unavoidable since it was present at the scene before the CSIs arrived. Some contamination, especially that caused by law enforcement can be avoided if not eliminated.
Some of the pollution that contaminates physical evidence is in the form of contributions made by those individuals present during the processing of the scene. Evidence technicians may contribute their own hair and fibers as they move about. They may have traces of soil, oil or grease on the soles of their shoes. Sometimes agency budgets are stretched to the point that disposable jumpsuits, head and shoe covers aren’t available.
Something can be done about the law enforcement-induced contamination. The place to begin contamination prevention is in the agency protocols and directives. Any agency that can expect to be called to investigate a crime scene should have written policies covering crime scene security.
The duty of the first officer or first responder on the scene is to preserve life and property. This would entail administering First Aid where necessary and removing victims from burning buildings. Once these steps are accomplished, then the scene must be secured. This means blocking access to the scene by anyone not essential to the evidence collection mission. Guards must be placed at all possible points of entry and an access log should be maintained showing who was permitted in and the time of access.
Avoiding crime scene pollution is the task of every individual entering the scene. This is a good reason why the audience present must be limited. Too many high profile cases have been lost in court due to limited or useless physical evidence.
