DNA Evidence: Measuring up to the Frye Standard of Acceptance

TrialDNA-based evidence has a long history of admissibility in legal proceedings stretching back to 1985 when Sir Alec Jeffreys first used DNA testing to resolve an immigration dispute in the United Kingdom. In 1987, DNA made more court appearances in parallel legal cases to convict serial rapist and murderer Colin Pitchfork in the UK and rapist Tommy Lee Andrews in the United States. Since these cases, the admissibility of DNA evidence in US courts has been challenged and upheld numerous times (United States v. Jakobetz and Andrews v. Florida), and DNA evidence has become the gold standard in many court cases. So why are scientists being asked once again to debate the admissibility of DNA evidence, specifically high sensitivity DNA, in the courtroom?

To understand, you must first know what the Frye standard is. Before evidence is admissible in a US court of law, certain standards must be met to ensure that the evidence is reliable and accurate. Obviously, we want to avoid wrongful convictions based on faulty science. The first set of US standards, which were adopted in 1923 in the case of Frye v. United States, requires that a scientific technique be generally accepted in the relevant scientific community. The Frye standard served the legal system well for many years. In 1993, during the federal case of Daubert v. Merrell Dow, the court ruled that the requirements set out in Rule 702 of the Federal Rules of Evidence superseded the Frye standard. This new standard, often referred to as the Daubert standard, requires scientific evidence and expert witness testimony to be relevant to the case and reliable. Many US states still use the Frye standard, which is considered to be more stringent, while others have adopted the Daubert standard. The legal hearing in which the court decides whether these standards are met is called a Frye/Daubert hearing.

Since the early days of DNA typing, when DNA “fingerprints” were generated using restriction fragment length polymorphism (RFLP) analysis, DNA evidence was ruled admissible because experts agreed that DNA typing is both scientifically accepted and reliable. In the 1990s, when STR analysis replaced RFLP, the legal transition was fairly smooth because individual aspects of STR testing—analysis of repetitive DNA sequences and PCR-based testing—had already met the Frye/Daubert standards. It was a period of great scientific achievement and relative harmony.

That changed when high sensitivity DNA testing (also known as low-copy-number DNA testing; LCN) entered the laboratory and courtroom. Debates about the validity and reproducibility of LCN testing were often heated; there would be no agreement about the reliability of this new type of DNA testing, which involves analyzing minute amounts of DNA (<100–200pg of total DNA). While some experts saw high sensitivity DNA simply as an extension or improvement of currently accepted procedures, others were concerned that the results generated using high sensitivity testing were much less reliable than results obtained using generally accepted methodologies (with recommended DNA amounts of 0.5–1ng). With strong debate raging in the forensic community, a Frye/Daubert hearing seemed inevitable.

And so it was. In November of 2014, high sensitivity DNA got its day in court. In this landmark case, Judge Mark Dwyer had to rule whether high sensitivity DNA evidence met the Frye standard. Many experts both for and against the new technology were called to testify, and it quickly became obvious that there was no consensus about high sensitivity DNA testing. Wisely, Judge Dwyer did not try to decide for himself whether the results from LCN are valid and reliable nor did he leave the decision up to a lay jury; rather, he let the inability of experts to agree make the decision for him. In his oral decision, Judge Mark Dwyer said:

“[M]y general views are not that there is anything that I can say is wrong with High Sensitivity Analysis or the [Forensic Statistical Tool] and I think it is a big temptation and a big mistake in a Frye hearing for a judge ultimately to decide which scientific techniques he thinks works. I don’t have the expertise for that and it is not my job in a Frye case to make that decision. It’s my job to see whether or not there is essentially general agreement in the scientific community as to the challenged scientific principles.”

He later added…

“[W]hy not put it before the jury and let the jury assess what weight should be given to the investigative leads that were developed? But it occurred to me ultimately that that’s inconsistent with Frye. To have a technique that is so controversial that the community of scientists who are experts in the field can’t agree on it and then throw it in front of a lay jury and expect them to be able to make sense of it, is just the opposite of what the Frye standard is all about. And so ultimately I had to think that it was inconsistent with Frye to give it to a jury when so many of the experts in the field don’t think that is appropriate.”

After all of the debate and deliberation, Judge Dwyer ruled that high sensitivity DNA does not meet the Frye standard of general acceptance.

What does this ruling mean for forensic labs in the US and around the world? This question is sure to generate a lot of discussion in the forensic community, as we try to fully understand the implications and consequences of this ruling. In fact, these discussions are already starting. At the 26th International Symposium on Human Identification (ISHI), forensic DNA expert Charlotte Word will be leading a panel discussion on LCN and admissibility. Don’t miss your chance to be a part of the discussions; be sure to register for ISHI, and join us in Grapevine, Texas, October 12–15, 2015.

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Terri Sundquist

Terri has worked as a Scientific Communications Specialist at Promega Corporation for more than 13 years, and prior to that, spent more than 5 years solving problems and answering questions as a Promega Technical Services Scientist. She graduated with B.S. degrees in Chemistry and Biology at the University of Wisconsin—River Falls, then earned her M.S. in Molecular Biology from the Mayo Graduate School in Rochester Minnesota.

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