Righting wrongs with DNA and PCR

Jeff Schmerker | Jan 3, 2022

The Takeaway: What happens when those deemed guilty are innocent? Polymerase chain reaction (PCR) technology, perfected over the years, has been responsible for freeing dozens of innocent defendants.

The Innocence Project and first DNA exoneration

Back in 1992, two young public defenders in New York City had an idea: If DNA could be used to convict someone of a crime, then it could be used in exonerations, too.

Barry Scheck and Peter Neufeld started the Innocence Project as a legal clinic at the Benjamin N. Cardozo School of Law in New York City. Lawyers and volunteers took on legal cases to free the wrongly convicted, and in 2004 the Innocence Project became an independent non-profit, though it is still associated with the Cardozo school.

Within years, high-profile exonerations had states rethinking their criminal justice systems. To date, there have been in excess of 350 exonerations based on DNA analysis, in part using PCR technology, more than 100 laws have been passed to prevent wrongful convictions and support exonerees, all 50 states have approved access to post-conviction DNA testing, and there are now 69 Innocence Network member organizations worldwide.

DNA “fingerprinting” was first performed in 1984 by British geneticist Alec Jeffreys, and by 1986 Jeffreys’ method had been used in court to free a boy who had falsely confessed to two crimes in England and instead ID the actual perpetrator. The first person in the U.S. exonerated of a crime by DNA evidence, also known as “DNA exoneration,” was Gary Dotson, in 1989; that same year David Vasquez became the first convicted defendant released from a United States prison on account of DNA testing.

How is PCR used in crime forensics?

The most popular DNA testing method used in exonerations is STR—the analysis of short tandem repeat regions on DNA, which today is considered the gold standard for DNA testing and the process most frequently used in DNA labs. Other popular methods include DQ Alpha, which uses a smaller amount of DNA; mitochondrial DNA, the analysis of DNA from a person’s maternal lineage; Y-STR, the analysis of DNA from a person’s paternal lineage which isolates the Y chromosome; mini-STR, which is the analysis of DNA from degraded or extremely small samples; and RFLP, restriction fragment length polymorphisms, the original DNA testing technique used in criminal justice, but one which required a large amount of DNA.

In the case of Dotson, the work of Jeffreys was inspirational but ultimately of limited assistance. Jeffreys's patented process, known as restriction fragment length polymorphism, required DNA of high molecular weight—high enough that that it would not work if the genetic material had lost mass due to degradation.

Polymerase chain reaction testing had the advantage of working on degraded samples, although its early applications were not perfect. Dotson, who had been accused of rape, was eventually freed after a 12-year ordeal; his accuser later told a psychologist that her vivid testimony was lifted from a novel.

Leading types of exculpatory evidence used in exonerations include intimate swabs, clothing, hair, fingernail evidence, bedsheets, and cigarettes.

Famous wrongful conviction cases exonerated by DNA evidence

Raymond Towler, who spent 27 years in prison for an assault and rape which occurred in Cleveland, Ohio, in 1981.
Ron Williamson and Dennis Fritz, accused of a 1982 Oklahoma murder, who each spent 11 years in prison; DNA evidence revealed the true murderer, who had testified against the defendants in the original trial. The case served as the inspiration for a John Grisham true crime book and Netflix series.
Darryl Hunt, who spent nearly 20 years in prison based on eyewitness testimony for a 1984 murder in North Carolina.

Thomas Haynesworth, who spent 27 years in prison for a 1984 case which The Washington Post called “one of the state’s most extraordinary legal cases.”
Michael Morton, who spent 25 years in prison for the murder of his wife; DNA tests linked another man to the murder and the prosecutor in the case was charged with contempt, lost his law license, and spent five days in jail after it was discovered he withheld evidence from the defense team.
Glen Woodall, who served five years in prison after circumstantial evidence pinned him to two crimes committed in West Virginia in 1987 and testimony by a lab tech was found to be falsified.
Jeffrey Mark Deskovic, who served 16 years for a murder in New York whose conviction was based on a coerced confession.
Five men known as the Dixmoor 5, imprisoned for a murder in Illinois later overturned when DNA excluded them as suspects; in 2014, they collectively won $40 million from the state for their conviction in a suit which alleged that police withheld exculpatory evidence, including DNA, from their defense teams.

Juan Rivera, who was convicted three times for the 1992 murder of an 11-year-old girl in Illinois based on a coerced confession riddled with factual inconsistencies obtained when he was in an acute psychotic state; after his exoneration, Rivera’s defense team found that the state had planted DNA on Rivera’s clothing from the actual killer. Rivera later received $20 million from the state.
Mark Maxson, who served 23 years for confessing to the murder of a six-year-old boy after being tortured and beaten by police interrogators.
Richard Alexander, who spent five years in prison based largely on eyewitness testimony for a spree of rapes in Indiana; mitochondrial DNA testing tied the crimes to another person.
David Camm, who served 13 years for the 2000 murder of his wife and two children in Indiana; it was later found that one of the key prosecution witnesses had lied about his credentials and training as a blood splatter analyst and had never worked a single case before; the defense team found that DNA evidence from the scene had never been analyzed even though prosecutors said it had.