Advertisement

The first information a crime scene investigator must look at is the “big picture:” What is the entire scene telling us? Just like assembling a jigsaw puzzle, we need to assemble a mental image of how all the pieces fit together. But we must also remain open to new information that may well change how the final picture looks when compared with our original assessment. If we are not open to re-evaluation, we develop tunnel vision and try to force the pieces together. Such an approach can cause us to overlook critical evidence that does not fit with our original ideas. In science, the final hypothesis is often different from the original premise. The flexibility to modify or abandon our original thoughts and develop a new theory or approach is critical to professionalism in crime scene work.

Owen McDonnell

The first information a crime scene investigator must look at is the “big picture:” What is the entire scene telling us? Just like assembling a jigsaw puzzle, we need to assemble a mental image of how all the pieces fit together. But we must also remain open to new information that may well change how the final picture looks when compared with our original assessment. If we are not open to re-evaluation, we develop tunnel vision and try to force the pieces together. Such an approach can cause us to overlook critical evidence that does not fit with our original ideas. In science, the final hypothesis is often different from the original premise. The flexibility to modify or abandon our original thoughts and develop a new theory or approach is critical to professionalism in crime scene work.

To avoid overlooking evidence, we must first recognize its value. A prime example of this problem is insects. Now, I acknowledge that some people really don’t like bugs and maggots. I once worked on a case where the death scene investigator had this exact problem. The body was some distance from the staging area, and he went with a patrol deputy to take a look. Unbeknownst to everyone, he had a can of bug spray in his pocket. He proceeded to spray the entire can of bug spray on the body to kill the bugs before anyone realized what he was doing. Let that sink in for a minute. Entomological (insect) evidence can prove invaluable to your case, but you need to be prepared to deal with it properly. In this article, we’ll take a look at forensic entomology and review what you need to know about this kind of evidence.

Forensic entomology is the application of the study of arthropods to criminal or legal cases. It can be divided into urban entomology, stored product entomology, and medical legal entomology. Insects and their predictable life cycles may help to establish the postmortem interval. Important conclusions may be drawn by analyzing the phase of insect invasion on the deceased by identifying the life stage of necrophagous (flesh-eating) insects in, on, or around the body. These conclusions must be made by a trained forensic entomologist, though such an expert rarely is available on the scene. Analysis requires not only knowledge of insect life cycles, but also knowledge of natural habitats and climate conditions that affect those specific insects. For example, if a body discovered in a densely wooded area has bugs that can’t exist in that environment, then you know the body has been moved. 

In cases where the body has undergone significant decomposition, limiting the kinds of testing a pathologist or medical examiner can perform, forensic entomologists can test the bugs or larvae for evidence of drugs and other substances. The primary use of forensic entomology, though, is in determining a time frame of death. Blowflies, which can quickly detect a decaying corpse, will travel to the corpse and then lay their eggs in the corpse’s eyes, ears, mouth, etc. They may also lay eggs in other dark, moist places, such as the folds of clothing or underneath the body. The eggs then hatch into larvae or maggots, which then turn into more adult blowflies. Eventually, other insects will also be drawn to the body. With an understanding of the type of insects present and their stages of development, a forensic entomologist can often provide a time interval for the death.

If your agency already has established a relationship with a forensic entomologist who can come to the scene, you are in luck. If you don’t have this option, you may be able to contact a forensic entomologist by phone and ask advice, or send him or her photos while you’re still on the scene. If neither is an option, you need to become familiar with collection and preservation techniques so that you can submit samples from the scene to an entomologist. Obtain procedural guides and manuals that show you what to look for and how to collect the bugs you find at a scene. Take a class that will give you some hands-on experience. 

Entomological collection kits are available that include materials for collecting and shipping specimens, and a list of forensic entomologists who can analyze the bugs. Perhaps the best part is each kit contains a set of detailed instructions that explains exactly what you need to do.

Some of the same rules apply to insects as applies to all other evidence. First, observe the scene and take careful notes. Pay attention to the type of environment and any special features you find there—rural or urban, indoors or outdoors, wet or arid, etc. Be specific about the location of the body, including position and compass direction. Record exactly where the insects are found and their type. Next, take and record the temperature at the scene. Temperature affects the growth of insects, so it is important to have a record of the temperature. Before you collect any specimens, photograph everything. Be sure to include close-ups of the bugs and their different stages.

After you have completed these steps, you can begin collecting samples. Make sure you collect samples of insects at every stage. If enough insects are present, collect some for preservation in solution and some live for rearing. When you collect samples, take them from the body and the area around it before it is removed. Once the body is moved, collect samples from directly under the body. Send all samples to a qualified forensic entomologist for analysis. (Again, consult a procedural guide or a collection kit for detailed information about the proper method for collection.)

CSIs face many challenges on scene, including those from extraneous sources. A crime scene can be chaotic when you first arrive. You may have to deal with people pulling you in different directions with multiple requests, radio traffic that becomes a distraction, supervisors requesting updates, weather conditions that cause concern—all while trying to establish a plan for your investigation. It is important to slow down, be methodical, and stay calm; doing so will allow you to come up with a systematic approach to the crime scene documentation and evidence collection. 

There are a lot of things that bug us on crime scenes, but insects shouldn’t be one of them. ●

Owen McDonnell retired as the Lieutenant/Supervisor of the Caddo Sheriff’s Office Crime Scene Investigations Division in Shreveport, LA after 31 years. He is the owner of M.O. Forensics LLC and provides consulting and training in crime scene and fingerprint development and comparison techniques, as well as heading workshops through IAI. He holds IAI certifications as a Senior Crime Scene Analyst, Ten Print Fingerprint Examiner and Latent Print Examiner. McDonnell holds a Master of Forensic Science Administration Degree from Oklahoma State University Center for Health Sciences.

Advertisement
Advertisement