How to Preserve a Crime Scene

It's hard to get a conviction without evidence, so preserve as much of the crime scene as possible.

Amaury Murgado Headshot

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The significance of being a first responder should never be lost on you. Because you are first, you have a huge list of responsibilities that compete for your attention all at once. One of the most important responsibilities you have involves the crime scene and its preservation.

The type of call you were dispatched to will help you determine where crime scene duties fall on your list of priorities. Let's face it, if the call is in progress, preserving the crime scene is not even on your radar at first. On the other hand, if the call is not in progress, then preserving the crime scene needs to become a part of every decision you make after you arrive.

General Considerations

If the call is in progress, you don't start anything with the crime scene until the dust settles. Your safety, as well as that of the victim and of those in the immediate area, is paramount. Your first priority is to do what needs to be done in order to obtain control of the situation and to render it as safe as possible. That includes providing first aid, removing victims from the scene, and finding the suspect. Everything else becomes secondary. However, you can't totally ignore the crime scene.

You should try to keep in mind how things appeared when you first arrived. Try to take mental notes if nothing else. If possible, record or write out your notes. This includes noting anything you had to move, rearrange, or break through to get in. Don't forget the power of your smart phone. You can use your cell phone's recorder, video, or camera features as long as you can use them without compromising your safety. Keep in mind that if you go the high tech route, the rules for handling evidence still apply to you and that information. You must follow your office policy.

You are responsible for reporting everything that happened regardless of the type of call you are on. It beginning as an in-progress call or you dealing with an emergency before the dust settled does not relieve you of that requirement. That being said, your initial involvement in crime scene preservation revolves around three basic duties: establishing a perimeter, finding out the suspects' movements, and keeping any unauthorized people out of the crime scene. Each one has its own focus that you must keep in mind.

Establish a Perimeter

There are really only two types of perimeters we ever deal with in law enforcement: the one we use to try to contain suspects to a certain area and the other, where we cordon off an area to preserve the crime scene. Although we work hard at the first one, we sometimes forget the importance of the second. Crime scene preservation and its importance can't be overstated, especially for first responders. Your actions, or lack thereof, will either help protect the crime scene or help destroy it. It's hard to get a conviction without evidence, so you need to preserve as much of the crime scene as possible.

The nature of your call will determine how large your perimeter needs to be. Most of the time, using crime scene tape will suffice. It's always better to go big at first because you can always shrink it down later. It never works out well the other way around. Keep in mind that on more serious calls or for scenes that cover a wider area, you might have to use road blocks, post officers at key points, or even use other governmental agencies' assets to help block off major roads, such as your version of the road and bridge department.

I handled a shooting one time at a large air-conditioned flea market spanning three separate connected buildings. Because it was a running battle that went from one end to another, the crime scene was huge. We had to shut down and control the entire complex for most of the day.

Suspect Movement

Another duty you have is to try to establish the nature of the suspects' movements. You need to establish where their point of entry was, how they moved inside, and where they exited. The exit point is especially critical because it helps you find their direction of travel. Screw that up and you have made tracking the suspect more difficult, if not impossible. If you can't secure anything else, secure the exit point because it will be a K-9's starting point. Keep everyone away from there until after the K-9 unit stops their track.

On one call, we were just minutes behind a mobile home burglary. We found a bloody towel just outside the residence that had obviously been used to smash through a window. Our K-9 team was second to arrive and I was sure we would catch the suspect unless they had escaped in a vehicle. As soon as we set up, the K-9 was off and tracking in a flash. To everyone's surprise, our K-9 team kept circling back to the residence and hung around one particular officer. It seems the officer had handled the bloody towel prior to our getting there. Our K-9 did his job but unfortunately the deputy that failed to secure the exit point (and touched the towel) did not.

Keep Unauthorized People Out

Once things are locked down, you have to control and record who comes in and out of your crime scene. You need to treat your crime scene like classified information: need-to-know basis only. If you are working the crime scene, you're in. If you are a gawker you're out. There is one notable exception, however. If you are a field training officer and exposing your recruit to something new, that's fine. Just make sure you clear it first.

There are a few procedures you can follow in order to limit unauthorized access. The first thing you can do is create a single guarded entrance. Everyone wanting to go in or out must pass through that point. You can also create a crime scene log. Anyone going in and or out is documented with the date, time, and the reason they went in. It's a good practice to advise officers that if they go in, they are subject to writing a supplemental report and that they may have to appear in court. Usually that's enough to keep away all but the most hardcore gawkers.

Where it gets tricky is when members of the command staff try to push their way in. I suggest you not argue with them, but I would make sure their entry is documented. It's been my experience that some members of the command staff only bother to show up for high-visibility crimes. For example, on every homicide scene I ever worked, it tended to look like a mandatory staff meeting. I don't care who they are; they walk into your crime scene, it gets documented.

Use Common Sense

There are other common sense considerations as well. For example, there is no eating, drinking, or smoking at a crime scene. If you are going to be there for a while, make sure you create a separate area for those things. And don't forget about members of the media. Your perimeter has to be big enough to prevent them from contaminating the scene.

Another aspect that is sometimes overlooked is protecting the crime scene technicians or the investigators themselves. Don't be so quick to clear the area and leave them alone if your suspects are still at large.

One resource I recommend on the topic is a PDF handbook on crime scenes by the National Institute of Standards and Technology (NIST). It's free and can be downloaded at  

Amaury Murgado retired a senior lieutenant from the Osceola County (FL) Sheriff's Office with over 29 years of experience. He also retired from the Army Reserve as a master sergeant and holds a Master of Political Science degree from the University of Central Florida.

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Amaury Murgado Headshot
Lieutenant (Ret.)
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