Crime Scene Contamination and the Amanda Knox Case
Lessons Learned for Law Enforcement
By: Joseph L. Giacalone
First, the investigator has to have the right mindset before investigating a major crime scene. They have to believe that this case will end up in a court of law. So they must painstakingly process the crime scene because contamination is unavoidable. The first officer on the scene begins the contamination process - it is just up to every other responder to minimize the damage. The case investigator must ask the first officer on the scene to take them on the same path that they initially took when they entered the crime scene. During the crime scene walk through, the investigator must walk in the patrol officer's "shoes" step by step. This will avoid disturbing any other evidence at the scene.
The biggest crime scene contamination problem is other officers. Investigating supervisors and case investigators must ensure that a patrol officer acts as the "Gate Keeper." The gate keeper's role is to prevent unauthorized personnel from entering the scene by maintaining a "Crime Scene Log." Everyone that enters that scene must be identified and recorded for a future court appearance. Most of the time the threat of being subpoenaed as a witness is enough to keep most "gawkers" out of your crime scene. The case investigator must obtain this log upon breaking down the scene and keep it with the case folder. The defense attorney will question you on who was at the scene and why they were there.
Another method of avoiding crime scene contamination is through the use of a "Crime Scene Assignment Log." The investigating supervisor must be able to keep track of where their people are at all times. This simple log will avoid the blunder of sending investigators from the primary crime scene to a secondary or tertiary one. Never send investigators from one scene to another because they will cross-contaminate the scenes. This is known as Locard's Exchange Principle - the basis of transfer between all objects. Inevitably an investigator will take something from one scene and leave it in the other. Do you remember how bloody the primary crime scene was in the O.J. Simpson case? It was quite easy for O.J.'s defense team to make the blood found in his home go away after pointing out that several investigators were at both scenes.
Crime scene technicians should employ single use tools when picking up evidence. Never use the same tools to pick up other evidence it will only taint its value. The technicians should also be inclusive - anything that appears to be evidence, is evidence. If you think it is, go with it and process it properly, because going back to a scene that has been released will provide enough reasonable doubt to twelve people that couldn't get out of jury duty.
However, there is a silver lining in this dark cloud. This case will serve as a law enforcement training tool and become a teachable moment of what not to do.
To learn more about criminal investigation, pick up a copy of the Criminal Investigative Function: A Guide for New Investigators.