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State lab testimony: analysts report DNA links between Pierre samples and Leonard Thompson
Summary
State and regional lab witnesses told jurors that DNA testing linked the defendant, Leonard Thompson, to several samples taken from the scene and from the victim, with mixed profiles showing varying degrees of statistical support.
DNA analysts testified that genetic testing on samples from the scene and the victim produced profiles that prosecutors say include the defendant.
Shanna Joseph, a forensic scientist with the Texas Department of Public Safety laboratory in Houston, testified that her unit received a case file and prepared evidentiary swabs and cuttings — including fingernail clippings and swabs from the couch and a kitchen lockbox — for DNA analysis. Joseph described the lab’s inventory and preparatory work and confirmed that a DPS lab case number (HOU231012916) was assigned to the evidence she prepared.
Michelle Turner, a DNA analyst at DPS who reviewed and interpreted the analytical results, told jurors the laboratory compared evidentiary samples to known reference swabs and a blood card from the victim. Turner testified to statistical likelihood ratios (LRs) used to weigh whether a given individual is a contributor to a DNA profile: she described some results as “very strong support” and others as “limited support.”
Turner summarized key findings in court: a partial profile from a couch swab strongly supported that the DNA came from Pierre; a swab from the exterior of a kitchen lockbox produced a mixture in which the LR provided limited support for Thompson as a contributor (LR ≈ 71); cuttings from a black-and-white plaid shirt were consistent with Thompson’s reference profile; a cutting from the shirt produced an uninterpretable result; two cuttings from Pierre’s white blouse matched Pierre’s profile; and fingernail clippings produced mixed profiles with differing weight — the left-hand clippings provided limited support for Thompson (LR ≈ 26) while the right-hand clippings returned a very large LR (described as about 76.6 octillion) providing very strong support for Thompson as a contributor.
Turner and Joseph explained the laboratory workflow (extraction, quantitation, amplification and analysis) and noted that multiple qualified analysts can touch different steps in the process. Turner described likelihood ratios as a statistical measure of how much more probable a profile is under one proposition versus another and cautioned jurors that such numbers do not map directly to population counts or to absolute certainty.
Defense counsel used cross-examination to probe the limits of the tests: analysts acknowledged that some samples produced only partial or low-template profiles, that presumptive serology is not definitive for blood, and that collection and handling steps and low quantities of DNA can reduce the weight of a comparison. The defense also raised laboratory-quality and audit questions; Turner said the lab maintains quality-audit procedures and documents incidents when they occur.
DPS exhibits containing the prepared fingernail kits and the blood card were admitted; the state also admitted a written laboratory report into evidence.
