Crime scene investigation involves protocols regarding taking photographs, collecting evidence and interviewing on-site witnesses. As DNA evidence becomes increasingly valuable in solving crimes, so does the need for stricter crime scene procedures that help protect DNA evidence from cross-contamination. Since the first person on the scene is often just an average citizen, it is important that the general public understand enough about DNA evidence to avoid contaminating the scene.
First step: Addressing Misinformation
Television shows featuring police officers, detectives, and crime scene investigators have been popular for a very long time. As fiction, they are entertaining and sometimes can be informative at the same time. Unfortunately, they can also give a false impression of what is and is not okay at a crime scene.
Consider the following example:
An investigator on a television show is at the scene of a crime. He is speaking with another investigator and leans back against a table, places his bare hand on the surface for support. In another room, a female detective runs her hand through her long brown locks and looks exasperated. Then she bends down over a victim, her hair nearly brushing the body. Her nose itches and she rubs it with a gloved hand.
I am sure most people can easily guess the mistakes made in that example. Properly trained investigators don’t touch anything at a crime-scene bare handed unless an emergency situation arises and there isn’t time to don gloves (for example, if a large lamp is about to fall on someone’s head). Investigators with long hair should keep it up, or wear a head covering. By touching her hair and her nose, the investigator has transferred her own DNA onto her gloves.
Taking precautions against contaminating DNA at the scene with outside DNA is very important. Little is at stake when actors in TV shows make these errors, but in real life, these kinds of errors can cause a lot of headaches back at the forensics lab, and can cost a lot of time, money, and even a case.
In some situations, investigators will wear Tyvek suits-disposable full body protective suits– which help to protect the scene from investigators’ DNA and protect the investigator from biological hazards. You won’t often see the star of a show in one of these– I agree that no one looks sexy in a Tyvek suit. Furthermore, real Tyvek suits are incredibly hot. They don’t look like they would be, but they are. In many crime scenes, however, protective clothing is necessary.
Objects at the scene and sources of DNA.
DNA evidence can be retrieved from many objects at a scene. These objects can include (but are not limited to), a weapon, flooring, bedding, laundry, telephones, remote controls, and counter tops. Sources include (but are not limited to) sweat, dandruff, mucus, saliva, semen, blood and hair. DNA evidence is often not visible to the naked eye. A telephone may, for instance, yield DNA evidence such as sweat, saliva, or other sources. Everyone knows that doorknobs can yield fingerprints, but they can also hold DNA evidence in the form of sweat or other sources. There are many objects at a scene that you might not assume hold any DNA evidence. There is usually no way for you to know, and so the best thing to do is avoid touching anything. Avoid sneezing or coughing as well, if you can.
What to Remember:
The chance that you will happen upon a crime scene may be slim, but in case you do there are things you should always remember.
1. Don’t touch or move anything if you can safely avoid doing so.
2. Make sure you are not in harm’s way.
3. Call emergency services immediately.
The same is advised if you are a victim of burglary. Avoid moving anything or touching anything and call 911 as soon as you can. If you have your cell phone with you, or are able to safely call from a phone in another house or business, do so in order to avoid contaminating DNA that might exist on the crime scene phone.
If you have moved anything or touched anything at the scene, be sure to let responding officers know.
DNA evidence is an incredibly valuable tool for catching criminals and, in many cases, for identifying victims. As technology improves (and DNA is analyzed more quickly), and existing technology is implemented in more regions across the nation, DNA evidence will play an even bigger role. By understanding how to avoid contaminating a crime scene, citizens can help, rather than hinder, a criminal investigation.
Note: Free on-line courses are available at DNA.gov as part of the President’s DNA Initiative. Courses are geared towards Law enforcement, Officers of The Court, and DNA Analysts. DNA.gov is a wonderfully informative site and I recommend that site for anyone interested in learning more about crime scene investigation and DNA. I’ve listed the link in the resources section of this article.