Date of Submission
Angie Ambers, Ph.D.
Extraction of Human DNA, Clandestine Grave, Decomposition Fluids, Real-Time (Quantitative) PCR
DNA, DNA Fingerprinting, Soil
DNA, DNA Fingerprinting, Soils--Testing, Soils--Analysis
Locard’s Exchange Principle states that “every contact leaves a trace.” The same principle applies when a perpetrator of a homicide decides to bury a victim in a clandestine grave. If a perpetrator originally buried a murder victim in haste to prevent discovery and then decided to later move the victim’s body to a remote location for disposal, decomposition fluids from the victim’s body (which contain cellular material and therefore DNA) would remain in the surrounding grave soil at the original burial site. It is possible that investigators could: 1) prove that a human body had once laid in that location (as opposed to animal remains), and 2) determine the identity of the victim via forensic DNA typing of the cellular remnants and body fluids left behind in the soil.
In this case study, a simulated clandestine grave was created in the laboratory using human remains (femur) from a previous cemetery exhumation. The remains were donated for research and had not been embalmed prior to burial. Over a 4-week period, the remaining soft tissue attached to the femur was allowed to decompose naturally; soil samples from directly underneath each femur section were collected at 1-week, 2-week, 3- week, and 4-week intervals. Two different DNA extractions methods (silica-based and organic) were performed in an attempt to recover human DNA from decomposition fluids in the soil. DNA quantities recovered from each soil sample aliquot were determined using a human-DNA-specific quantification kit and real-time (quantitative) PCR. The organic extraction method yielded higher amounts of human nuclear DNA for downstream STR genotyping than silica-based DNA extraction. The average DNA quantities (ng) recovered using organic and silica-based DNA extraction were 1.6929 ng and 0.0445 ng, respectively. Although attempts were undertaken to purify DNA and remove PCR inhibitors from the soil (e.g.,acids, fulvic acids), qPCR results indicated that many samples were still exhibiting signs of inhibition. Although this study demonstrates proof-of-concept that human DNA can be recovered from decomposition fluids in soil underneath human remains in clandestine graves, future research efforts should focus on improving DNA extraction approaches that would better facilitate removal of soil-derived inhibitors
Lopez, Arely Joaly Parra, "Extraction of Human DNA from Soil in a Simulated Clandestine Grave" (2021). Honors Theses. 15.