Trace DNA uses STR analysis to identify skin cells or other tiny specimens of human genetic material left behind at a crime scene.
In court, defense teams can protect clients against life-changing charges by pinpointing whose DNA was at the scene.
The scientific process of STR analysis
Short Tandem Repeat (STR) analysis allows scientists and investigators to confidently differentiate one strand of DNA from others. By looking at repeating sequences of gene alleles and using mathematical probability calculations, STR can identify a person’s DNA with statistical accuracy. A 2020 study from the National Center for Biotechnology Information summarized a legal case in which there was a 100% match between a PCR saliva swab and DNA found at the crime scene.
Challenging criminal charges and convictions
Numerous high-profile clients have successfully used STR analysis and trace DNA to beat their charges. STR cleared JonBenet Ramsey’s parents of their murder charges after DNA evidence on Ramsey’s clothing was a mismatch for both parents. A teacher named John Mark Karr was also cleared of suspicion when DNA evidence at the scene showed the presence of a male, but no DNA belonging to Karr.
In a separate case involving Lukis Anderson, even though investigators found his DNA at the crime scene, scientists determined that his DNA had transferred there inadvertently. The same EMTs who responded to an unrelated scene with Anderson earlier in the day later responded to a murder scene.
Trace DNA is therefore a valuable asset in criminal defense, appeal and post-conviction cases.