For the past six years, environmental scientist Jacqui Aitkenhead-Peterson has been assisting law enforcement by matching soil from crime scenes and suspects and determining evidence of human decomposition products. This year, thanks to Michael Ben Alexander, she added someone special to her team.
When law enforcement brought Peterson a large number of samples to analyze for a case, she knew she had to bring in reinforcements. So, she called Alexander, one of her graduated Ph.D. students. Alexander trains human remains detection dogs (HRD) at the Forensic Anthropology Center at Texas State (FACTS), where he established the cadaver dog training program in 2013.
Human remains detection dogs are trained to “hit” on smells associated with decomposing bodies that are often undetectable to the human nose.
“Dogs have a significantly higher sensitivity than the equipment in my lab,” Peterson told Forensic. “[For this case], the number of samples collected by law enforcement was numerous so it is useful to have trained HRD dogs alert for human remains before time-consuming chemical analyses is performed.”
If the HRD dogs show interest, the next step for Peterson is to scan sub-samples of the soils using UV-Vis-NIR spectroscopy. Peterson created a model based on different NIR wavelengths to find a match between a selection of solids, including soli from the suspect, the crime scene and controls. Typically, the diffuse reflectivity of decomposition-contaminated soils is significantly lower than regular soil, as corpses leave high concentrations of carbon, nitrogen and phosphorus. These UV-VIS-NIR results indicate to Peterson whether she needs to continue with wet chemical analyses to determine cadaver decomposition islands (CDI).
“Published methods typically examine soil at 0 to 5 cm or 0 to 10 cm depth,” Peterson explained. “In order to estimate a better post-mortem interval, I take deeper soil cores and split them into 0 to 10 cm increments to take into account the transport of decomposition products down the soil profile.”
Currently, Peterson is collaborating with Retego Labs (Utah) to develop methods to extract soil and quantify soil chemistry in CDI’s onsite. As with other onsite forensic analyses, this would help speed up the investigation.
As an environmental scientist with a focus on soil and surface waters, partnering with law enforcement was not in Peterson’s immediate plans. Rather, it happened accidentally out of Peterson’s desire to recruit more undergraduate students to soil science programs. In a novel way to increase interest, the Texas A&M professor developed the course “Forensic Soil Science” in 2009. The course was a success and eventually led to Peterson conducting research and teaching workshops at the body farm at Sam Houston State University.
“Early workshops on how to collect and analyze soil at outdoor crime scenes were attended by law enforcement personnel and that evolved to my first case, which was to match soil from the gas pedal of a vehicle to soil at a suspected crime scene.”
The partnership has only grown from the initial case six years ago. In that time, Peterson’s coursework has grown, as well. The course is billed under both the Forensic & Investigative Sciences Program and the university’s Soil & Crop Sciences program. It typically comprises mostly students from the forensic program, and two or three from the soil department.
“Overall, I was to expose forensic students to soil as trace evidence and expose soil students to forensics and the potential of soil to be used in other fields,” Peterson said.
Photo: A human remains detection dog trained by Alexander signals a “hit.” Credit: Texas A&M AgriLife/Beth Luedeker