Probabilistic genotyping and the power of modern DNA technology: A case study in overturning a wrongful conviction for murder in Texas

C.E. Credits: P.A.C.E. CE Florida CE
Speaker
  • Assistant Director, Henry C. Lee Institute of Forensic Science, Associate Professor, Forensic Geneticist, Henry C. Lee College of Criminal Justice & Forensic Sciences, University of New Haven
    Biography
      Dr. Angie Ambers is Assistant Director of the Henry C. Lee Institute of Forensic Science, a world-class institute that specializes in interdisciplinary research, training, testing, casework consulting, and education in forensic science. She also holds an Associate Professor appointment in the Henry C. Lee College of Criminal Justice and Forensic Sciences at the University of New Haven, teaching basic and advanced forensic DNA analysis methods. She has a Ph.D. in molecular biology (with emphasis in forensic genetics and human identification) as well as master's degrees both in forensic genetics and in criminology. Dr. Ambers is an active cold case consultant, an advocate of post-conviction DNA testing, and an educator/advisor on DNA testing or re-testing of old, degraded, or challenging evidentiary samples. Dr. Ambers specializes in genetic characterization and identification of contemporary, historical, and archaeological human skeletal remains. Her casework has involved DNA testing of an American Civil War guerrilla scout, Finnish World War II soldiers, unidentified late-19th century skeletal remains discovered by a construction crew (Deadwood, SD), Special Operations soldiers killed during the 1974 Turkish invasion of Cyprus, skeletal remains exhumed from Prague Castle (Czech Republic), soldiers from the Seven Years' War (1756-1763), bones of a Jesse James' gang member, remains associated with the French explorer La Salle's last expedition, and Spanish Royal bones (Kings of Aragon). She has traveled to India to train scientists from various Indian states and the Maldives Police Service on the processing of bone samples in forensic DNA casework. Her casework and research has been published in various peer-reviewed journals [Forensic Science International: Genetics (FSI: Genetics), International Journal of Legal Medicine, Legal Medicine, BMC Genomics, Croatian Medical Journal, The Journal of Heredity] and has received press in numerous local and national newspapers, including The Washington Times. In addition to skeletal remains cases and research, Dr. Ambers was Project Lead on a U.S. State Department grant (2017-2018) to combat human trafficking in Central America through the application of forensics. She traveled to three Northern Triangle countries (Guatemala, El Salvador, Honduras) to perform gap assessments of government laboratories and train personnel in forensic DNA analysis. In addition, she was part of a consortium to help these countries develop/maintain forensic DNA databases to assist in identification of missing persons related to human trafficking.

    Abstract

    In late 2019, nearly a decade into a life sentence, Lydell Grant was released from a Texas prison after being convicted of a murder that he did not commit. The victim, Aaron Scheerhorn, was stabbed multiple times in a parking lot outside of a bar in Houston. A DNA mixture was recovered from the victim’s fingernails but was too complex to analyze at the time of the original trial. Mr. Grant’s conviction resulted primarily based on the testimony of six eyewitnesses, all of whom identified him as the killer. During the trial and the entirety of his imprisonment, Grant vehemently denied his involvement in the crime. In 2018, forensic DNA expert Dr. Angie Ambers and a legal team from the Innocence Project of Texas requested access to evidentiary samples collected from the victim during autopsy. Mixed DNA data generated from the victim’s fingernails was sent for analysis using a “probabilistic genotyping” software program called TrueAllele®. Analysis of the raw data from this DNA mixture not only excluded Mr. Grant as the source of the foreign DNA, but resulted in a CODIS database hit that identified the actual murderer of Mr. Scheerhorn. This presentation will provide an overview of Grant’s case, as well as a discussion of subjectivity issues with previous DNA mixture interpretation approaches and the improved (more  objective) analytical capabilities provided by probabilistic genotyping software programs.

    Learning Objectives:

    1. Identify issues regarding DNA mixture interpretation

    2. Learn about current probabilistic genotyping programs for forensic casework

    3. Understand how probabilistic genotyping can assist with post-conviction DNA testing


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