The Silent Witness: 20 Best Practices for Processing a Crime Scene

Since the beginning of time, man has searched for witnesses to crimes. In the Bible, the first instance of criminal interrogation occurs when the Lord asks Cain, “Where is your brother?” In his response—“I don’t know; am I my brother’s keeper?”—we have the first instance of perjury. Even then, so many years ago, criminal evidence proved critical: “What have you done?” the Lord said. “The voice of your brother’s blood cries out to me from the ground.” The blood of the victim bore silent witness to the suspect’s crime.

First responders train constantly. They train for civil disputes, domestic violence, hostage negotiations, how to set up perimeters, contacting barricaded suspects, resolving conflict, rendering emergency aid to both citizens and partners, and much more. The reason for all this training is twofold: 1) When first responders arrive on scene, they must implement best practices without giving much thought to what they are doing, and 2) training helps us resist the tendency to fall into bad practices.

Remember Locard’s Exchange Principle: Every perpetrator of a crime will bring something into the crime scene and leave with something from it. Both can be used as forensic evidence.

The same principle applies in the identification and collection of physical evidence. It is all too easy amidst the commotion and chaos of a crime scene for the plans to change, for our original thoughts and intents to be clouded, and for important matters to be overlooked. The primary officer has the responsibility to assess the scene; call for support; direct the support where needed; set up perimeters; close off routes of ingress and egress; ensure the safety of victims, witnesses and other first responders; and finally, but just as important, identify evidence and see that it is collected and processed properly.

If your agency employs evidence technicians and/or crime scene investigators, remember, the crime scene is the officer’s responsibility. Brief evidence techs/investigators on details, work with them as a team and communicate openly. For evidence to be useful in court it must be discovered and collected legally, documented properly, collected properly and properly identified in court. And for that to happen, officers must train on proper techniques for securing and processing crime scenes. As Aristotle said, “We are what we repeatedly do. Excellence, therefore, is not an act but a habit.”

Best Practices

Following are some best practices to consider for processing a crime scene:

  • Secure the scene. Determine where you will put up your barrier tape. How big do you need your scene to be? Once you decide, make it bigger; in fact, make it even bigger than that. You can always reduce it, but once you start, you can rarely expand it.
  • Secure weapons, but only if they are a threat or danger to you or someone else. If not, let them stay where they are, untouched.
  • Establish one way in and one way out. This will eliminate unnecessary tracking all over your scene.
  • Only allow those inside the crime scene who have a need to be there and a right to be there. Remove victims and witnesses and maintain a secure, uncontaminated scene as soon as possible and for as long as necessary.
  • Start a crime scene log and maintain it. No one enters the crime scene without signing the log. This can be very important later in the investigation.
  • Note who was in the scene when you got there, where they were and what they were doing.
  • Note any alterations to the scene that may have occurred from firefighters, EMTs, other officers, etc.
  • Note lights on or off, television on or off, air conditioner or heater on or off, windows open or closed, etc. These details can be very important.
  • If you aren’t sure if something should be collected as evidence, take it. It’s easier to give it back than to try to get it later and then prove it wasn’t compromised during the time you left it.
  • Think about the possibility of a second scene. Is it secure? By who
  • Never add anything to the scene unless absolutely necessary. This means no chalk outlining evidence or a victim’s body. Resist your urge to mark evidence unless absolutely necessary.
  • Never cover a body with a blanket or other object that may introduce trace evidence into your scene or onto the body. In most cases officers and investigators are not allowed to touch the body. Covering it will only delay the process for evidence recovery while waiting on the coroner.
  • Remember Locard’s Exchange Principle: Every perpetrator of a crime will bring something into the crime scene and leave with something from it. Both can be used as forensic evidence. This applies to you as well.
  • Is there any perishable evidence, such as impressions, loose paper money, etc.? Is it secure?
  • Always wear gloves and be careful talking inside the crime scene. Databases are full of unknown fingerprints and DNA belonging to first responders.
  • Observe the scene and conditions. Use your sense of smell, hearing and eyesight. Pay attention to the details, understand what you are seeing and make notes as you go.
  • Think about where DNA could be. Even smeared fingerprints still leave good DNA evidence. It’s very difficult to be inside a crime scene and not leave DNA or trace evidence behind. Think outside the box.
  • Put yourself in the suspect’s shoes: Where did they go, what did they do, where did they leave evidence that they were there?
  • Never use the telephone, bathroom or trash cans inside a crime scene. Never eat, drink or smoke inside a crime scene.
  • Always do a final walk-through. Has everything been done, did you leave anything behind? Discuss details, secure the scene, tear down the crime scene tape and never leave your trash. Take your crime scene tape with you to avoid having to go back when a call comes in that your yellow barrier tape is all over the neighborhood.

Unusual DNA Cases

In my career, I worked hundreds of scenes for evidence, and each one was a little different. Here are two interesting cases from colleagues of mine that really stand out: The owner of a vehicle involved in a DUI claimed she was not driving her vehicle. Someone else must have taken her car, drove it drunk, and hit someone, injuring them. The impact was enough to cause the airbag to deploy. The evidence technician processing the vehicle found the airbag deployed and examined it for any possible evidence. She found the outline of a pair of lips with lip gloss on them. She cut out the air bag and submitted it for DNA evidence. You can guess what the results were, right? Sure enough, the lip prints left behind belonged to the registered owner of the vehicle. She was unaware the force of the bag deployment caused it to hit her in the face, where she left her DNA behind.

Another unusual DNA case involved a residential burglary where the victim came home while the suspect was inside his house. Standing at the front door, the suspect saw the victim and ran out the door right in front of him. As he did, the victim slapped him across the face. The evidence technician who responded to the scene overheard the victim telling the officer how he slapped the suspect as he ran by. Thinking outside the box, she asked him if he had washed his hands yet. He had not. She then collected a DNA swab from the victim’s hand and submitted it. The sample identified the suspect.

These are just a couple cases where the crime scene investigator went the extra mile to obtain evidence. Our motto is, if it’s there, we will find it. Paul Kirk, considered the father of modern forensic science, said it best:

Where he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as silent evidence against him. Not only his fingerprints or his footprints, but his hair, the fibers from his clothing, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen that he deposits or collects; all these things and more bear mute witness against him. This is evidence that does not forget. It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong; it cannot perjure itself; it cannot be wholly absent. Only its interpretation can there be error. Only human failure to find, study, and understand it can diminish its value.

Shirl Tyner

SHIRL TYNER is a Management Services Representative for Lexipol and has 25 years of law enforcement experience as a civilian (non-sworn) employee, serving with the Oceanside (CA) Police Department and the Tustin (CA) Police Department. Her tenure included positions as front desk officer, field officer, report writer, field evidence technician, crime scene investigator and fraud investigator. In many of these areas she held supervisory positions, and she served as a field training officer for 20 years. Shirl has experience as a Trauma Intervention Volunteer and has been heavily involved in peer support, with a special focus on PTSD. A graduate of the Los Angeles County Sheriff’s Department Deputy Leadership Institute, she has a bachelor’s degree in Psychology and a Graduate Certificate in Forensics and Crime Scene Investigations and is currently working on a master’s degree in Forensic Science. Shirl teaches Criminal Justice and Forensic courses at both the high school and college levels.

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