Student question: What steps do CSIs need to take to preserve a crime scene? Are there special steps when collecting evidence?

I've outlined the steps below. Remember each agency is different and the steps may be differ from what is written.

For Scene Preservation:

This is one of the most important parts of an investigation and often inadequately managed by first responders. When you arrive at the scene several police officers and firefighters have come and gone. Never assume that the crime scene before you has not been altered in some way.

1. Park your vehicle well outside of the scene perimeter. Once you have confirmed the perimeter is enough and/or have progressed in the investigation, you can move your vehicle closer or to a better location.

2. Contact the officer managing the investigation and obtain all pertinent information regarding the scene. Be sure to ask if anything has been moved, removed or otherwise altered.

3. Determine if the perimeter is enough in size or if it needs to be increased. The perimeter can be decreased as the investigation progresses however never decrease the perimeter at this stage of the investigation.

4. Have all unnecessary personnel leave the scene.

5. Identify hazardous conditions that exist within the scene, i.e. curbs, holes, hanging wires, etc. and take steps to eliminate or avoid them for your safety.

For Evidence Collection/Preservation:
Certain weather conditions can alter or destroy evidence. Preservation of the evidence is paramount.

1. If the evidence is secure (weather is not a threat) begin the next step.

2. In the case of inclement weather only the evidence that would be adversely affected should be collected immediately. Always place an evidence placard next to the item prior to collecting it to mark its position. If the weather permits, photograph the evidence prior to collecting it.

A great resource for overall crime scene investigation guide, Crime Scene Investigation, A Guide for Law Enforcement, can be found here, at the National Institute of Standards and Technology (NIST). It's a free PDF for you to download.