Using Forensic Entomology to Help Establish Time of Death
Start a criminal justice degree at American Military University.
Forensic entomology is the science of collecting and analyzing insect evidence that can help approximate how much time has passed between when a person died and when their body was discovered. This period of time is referred to as the post-mortem interval or PMI. Entomology is also useful in determining whether a body was moved after death and may provide investigators clues about the circumstances surrounding the death.
How Forensic Entomology Assists Death Investigations
As soon as a human dies, the body begins to decompose. However, signs of decomposition are not usually visible to the naked eye until many hours after death. Insects, however, have a keen ability to sense the liquids, gases, and chemicals emitted from a dead body and are quickly attracted to these by-products of decomposition.
Though many different types of insects flock to a dead body, flies and beetles are most useful in determining the PMI. Specifically, blow flies and house flies are two of the most common species to inhabit a dead body. These insects are usually attracted to a dead body within 10 minutes following death and begin laying eggs soon after. They seek out natural body openings (eyes, nose, mouth, ears, and genitals) and open, bloody wounds to lay eggs in because wetter environments are ideal for the incubation and hatching of their larvae, known as maggots.
The eggs incubate, on average, for 12-24 hours, after which maggots can be observed. Maggots have a rapid life cycle in which they go through five stages, called instars. The rate at which they progress through the instars varies slightly depending on the species and environment they are exposed to. Generally, however, they reach the third instar within four to five days. This phase lasts several more days before the maggots enter the fourth and fifth instars, where they burrow into surrounding soil to pupate and then emerge as grown flies.
It’s important to note that flies and other insects will continuously flock to a dead body in the days after death; they won’t all arrive at the same time. Therefore, it is normal to find maggots of differing sizes on a body that has lain in the elements for several days. It is critical for investigators to look for and measure the largest maggots since the most mature maggots were laid first and provide the most accurate indicator of the PMI.
Applying Forensic Entomology to Rebekah Gould’s Murder
I’ve written several articles analyzing the known evidence in the 14-year unsolved murder of 22-year-old Rebekah Gould (learn details of the case starting with my first article). In the fifth article in the series, I touched on the use of forensic entomology to help determine her day of death.
According to her autopsy report, the maggots found on Rebekah’s body measured between 1/16-inch and ½-inch long. The report does not include any further information or analysis about maggot or other insect activity at the processing of the disposal site where her body was found or later at the autopsy. As stated above, flies continue to flock to a dead body in the days after death and lay their eggs, so the logical conclusion is that the largest maggots found on Rebekah’s body measured half an inch long.
An independent review of her autopsy (requested by one of her family members several years ago) provided further insight by stating that, based on the maggot size and average ambient temperature, the maggots grew for 6.25 days. Knowing Rebekah was found and pronounced dead at approximately 11:00 a.m. on Monday, September 27, 2004, the maggot growth indicates they hatched during the very early morning hours of Tuesday, September 21, probably somewhere around 5:00 a.m. It’s important to keep in mind that this time is variable by a couple of hours in either direction.The required incubation time for eggs (12-24 hours) indicates her body was placed at the disposal site between 5:00 a.m. and 5:00 p.m. on Monday. We know Rebekah was alive around 8:30 a.m. on Monday since there is video footage of her from a convenient store. This information narrows the window of time during which the killer disposed of her body.
This window can be confirmed due to the warm temperatures Arkansas experienced the week after Rebekah’s death. That particular week had an average ambient temperature of 75 degrees Fahrenheit (25 degrees Celsius) with high humidity (85 to 95 percent) each day. Temperatures of this level accelerate the insects’ egg-laying, incubation, and hatching process. The incubation period likely took between 12 to 18 hours (shorter than the potential of 24 hours). The reported maggot size is consistent with her body lying in the elements for this many hours prior to the maggots hatching. This provides additional evidence that her body was left at the disposal site prior to 5:00 p.m. on Monday.
Unknown Variables Affecting the Entomology Evidence in Rebekah’s Murder
There are several unknown variables that could impact the entomology evidence in Rebekah’s murder. For example, it is unknown at exactly what time maggot(s) were collected from her body. Ideally, insects should be measured immediately when the medical examiner (ME) arrives at the location of a body. However, it’s possible the collection and measurement was not completed until after Rebekah’s body arrived at the ME’s office. If this was the case, the maggots would have had additional time to grow before being measured.
Also, the autopsy report does not state what type of maggot(s) were found and collected. Different insect species have varying temperature requirements for ideal growth rate. Without knowing the species of maggot found on Rebekah’s body, we cannot determine exactly how weather conditions affected their growth rate. In general, however, the hotter the average ambient temperature, the faster maggots grow.
Conclusions Drawn from Entomology Evidence
Both the official autopsy report and the independent review of the report indicate that Rebekah’s body lay in warm ambient temperatures for at least six days. It is important to remember that although she was likely attacked between 8:30 a.m. and noon on September 20, 2004 (the interval between when she was last seen alive and when she was due to pick-up her sister), she may not have died right away. As discussed above, her body was likely placed at the disposal site between 9:30 a.m. and 5:00 p.m. on Monday. It’s very possible she lay unconscious, but alive, for several hours after being left. Therefore, the arrival of flies may have been delayed.
We can also conclude it is unlikely that her body was stored in an enclosed space (e.g., trunk of a car or in a suitcase), for any significant amount of time after she was killed and before being transported to the disposal site. The maggot growth does not support this scenario. Had her body been stored somewhere enclosed, it would have taken many more hours for the flies to detect and gain access to that location.
It is also unlikely Rebekah’s body was moved more than once after she was killed in Casey McCullough’s house. Even if her uncovered body was first moved to an outside environment where insects could find it soon after death, the killer would have disrupted the egg-laying process by moving it a second time. Though some eggs would have remained, the majority of the egg-laying cycle would have started over at the location where her body was finally left. If she had been moved more than once, I would have expected the medical examiner to find maggots with a smaller size (i.e., having had a shorter life span than 6.25 days) than those described in the autopsy report.
Therefore, the entomology evidence supports the conclusion that Rebekah was moved to the disposal site where she was found a week after she was attacked and killed at Casey McCullough’s house. It also supports the timeframe that she was killed on September 20, 2004 and left at the disposal site sometime between 9:30 a.m. and no later than 5:00 p.m.
I suspect her body was moved much sooner than that, however, as the killer probably disposed of it directly after the hasty clean-up of the crime scene. It would not have made sense for him to leave her body in the house after cleaning (this would have led to another mess to clean up, plus the risk of being discovered by someone looking for Rebekah) and it’s doubtful he left her in his vehicle unattended. It’s possible he placed her in an outbuilding or in the woods near Casey’s house and came back later to move her, but this also seems unlikely. Based on the maggot activity, we can deduce that her body was moved during daylight hours (by 5:00 p.m. on Monday, at the latest), so there would be no reason to move her twice; doing so would only create more risk for the killer, with no advantage.
Using forensic entomology in cases like Rebekah Gould’s murder can help investigators estimate the time of death as well as provide supporting evidence about whether or not a body was moved after death and approximately what time it was moved. It can also indicate areas of injury on a body, which may present insight into the cause or manner of death in some cases. Combined with other case facts and investigative evidence, entomology can be an extremely helpful tool for death investigators and homicide detectives.
About the Author: Jennifer Bucholtz is a former U.S. Army Counterintelligence Agent and a decorated veteran of the Iraq and Afghanistan wars. She holds a Bachelor of Science in criminal justice, Master of Arts in criminal justice and Master of Science in forensic sciences. Bucholtz has an extensive background in U.S. military and Department of Defense counterintelligence operations. While on active duty, she served as the Special Agent in Charge for her unit in South Korea and Assistant Special Agent in Charge at stateside duty stations. Bucholtz has also worked for the Arizona Department of Corrections and Office of the Chief Medical Examiner in New York City. She is currently an adjunct faculty member at American Military University and teaches courses in criminal justice and forensic sciences. Additionally, she is a licensed private investigator in Colorado. You can contact her at IPSauthor@apus.edu. For more articles featuring insight from industry experts, subscribe to In Public Safety’s bi-monthly newsletter.