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Seven Crime Scene Fundamentals

Seven Crime Scene Fundamentals

Lieutenant Raymond E. Foster, LAPD (ret.)

Crime scene protection is one of the basic, yet critical aspects, of field police work. Good crime scene practices enhance criminal investigations and, ultimately prosecutions. In this article, we explore seven aspects of crime scene protection that will improve your skills.

What is a crime scene?

If you ask most law enforcement professionals, they will likely tell you a crime scene is a location in which a crime occurred. This is an inadequate description. A crime scene is any location, person or thing wherein evidence of a crime may exist. Suppose you respond to a body dump. You have a homicide victim who has been dumped along the side of the road. Based on the investigation it is determined that the individual was murdered elsewhere. So, you have at least four crime scenes: the dump location, the murder location; the vehicle used to transport the victim; and, the victim’s body.

Later during your investigation you identify a offender and your investigation leads you to prepare a search warrant for his home. You know the murder occurred at a warehouse and not the offender’s home, however. If you prepare a search warrant, you will be searching for evidence that would tend to incriminate the offender. However, if the murder didn’t occur in the offender’s home, the offender and the offender’s house might still contain evidence of the crime of murder and therefore they are crime scenes. All of these particular crime scenes – body dump location, vehicle, murder scene, the victim’s body and offender’s home should have the same level of crime scene protection.

The concept that a crime scene is any location wherein evidence of a crime may exist impacts nearly every action a patrol officer takes. Consider that a traffic stop that develops into a felony arrest means the violator’s car (and the violator) may be crime scenes. Your next domestic violence call may be a crime scene, also.

Field Tactics at a Crime Scene

Field tactics are those defensive and offensive strategies, devices and procedures that increase police officer, citizen and offender safety. Field tactics always trump crime scene protection. One paramount and sometimes overlooked field tactic is a thorough search for the offender at the crime scene before crime scene protocols are initiated. If there is a victim down inside a location, the rescue and immediate medical care of that individual is more important than the crime scene. Another example would be the service of the search warrant at a murder suspect’s home. The evidence is not worth anyone’s safety.

Once you put up the yellow tape, follow-on personnel assume the scene has been cleared for the offender. I responded to crime scene where homicide detectives where cataloguing evidence hours after the initial call and they were surprised, and overpowered by the suspect who had secreted himself in a kitchen cabinet. As a first responder, it is your job to balance the protection of all personnel against the need to initiate good crime scene protocols.

The Theory of Transfer

In the late 19th Century, Dr. Edmund Locard, was one of the first criminalists. Locard, a French physician, developed the Theory of Transfer which is also referred to as the Exchange Principle. In essence, Locard said that whenever two objects come into contact with one another, they each leave and take something. There is always evidence of the exchange. Locard’s theory is the foundation of all good crime scene protocols.

Think of a traffic collision. How often have you noticed paint transfer on each of the vehicles involved? The paint transfer is an example of Locard’s theory – each vehicle has left something of itself on the other vehicle. At a crime scene we are locating, documenting and recovering evidence of a transfer between the offender and the location. Offenders leave something of themselves at the crime scene: fingerprints; DNA; footprints; etc. The offender also takes something from the crime scene: fibers; soil; DNA; etc.

Crime Scene Protection

One of the reasons we put up the yellow tape and deny entrance to crime scenes is Locard’s theory. Each person who enters a crime scene – paramedics, first responders, detectives and other personnel – leave something of themselves and take something from the crime scene. No matter how careful someone is, if they enter a crime scene, Locard’s Theory says they contaminate it.

We minimize contamination in three ways: denial of entrance; use of protective gear (gloves and booties as an example); and, by the use of a crime scene log. The first two are probably obvious. If you don’t go in the crime scene, you can’t contaminate it. If you do go in, and you wear the proper protective equipment you are less likely to leave something of yourself, such as fingerprints, at the crime scene. The third method, a crime scene log, helps us eliminate evidence later. If you find Sergeant Smith’s fingerprints at the crime scene it is much more likely he left them there during the investigation than during the crime itself. His fingerprint can likely be eliminated because our crime scene log tells us he was there.

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