HIGH PROFILE CELEBRITY TRIALS AND CRIME TELEVISION SHOWS SUCH AS CSI HAVE HAD A MONUMENTAL EFFECT ON RAISING PUBLIC (AND CONSEQUENTLY, JURY POOL) AWARENESS OF DNA’S ROLE IN THE CRIMINAL INVESTIGATION PROCESS. DESPITE ITS MORE RECENT DRAMATIC APPEAL, THE USE OF DNA EVIDENCE HAS UNDERGONE A CAREFUL, STEADY EVOLUTION TO BECOME A STANDARD FORM OF ADMISSIBLE EVIDENCE IN TODAY’S COURTROOMS.

The extensive scrutiny that has been placed on DNA evidence over the years is due not only to the relative newness of the technique in the judicial system, but also to the sheer power of DNA to discriminate between individuals and hence to convict or exonerate.

In recent years, legislative issues have become the focus, stemming from the increased use of DNA databanking and the movement to allow post-conviction DNA testing.

Early Days

DNA profiling was originally developed as a method of determining paternity, in which samples taken under clinical conditions were examined for genetic evidence that could link parent to child. It first made its way into the courts in 1986, when police in England asked molecular biologist Alec Jeffreys, who had begun investigating the use of DNA for forensics, to use DNA to verify the confession of a 17 year-old boy in two rape-murders in the English Midlands. The tests proved the teenager was in fact not the perpetrator and the actual attacker was eventually caught, also using DNA testing.

The first DNA-based conviction in the United States occurred shortly after in 1987 when the Circuit Court in Orange County, Florida, convicted Tommy Lee Andrews of rape after DNA tests matched his DNA from a blood sample with that of semen traces found in a rape victim.1 The first state high court to rule in favor of admitting DNA evidence came two years later in West Virginia.2

In the first years following these groundbreaking cases, the admissibility of DNA evidence was not largely disputed. That began to change once the technique began to become more widely used by prosecutors. Soon defense attorneys began challenging the admissibility of DNA tests.

Admissibility Standards

In general, two standards are used to judge the admissibility of novel scientific evidence - the “Frye standard” and the “Daubert standard.” The Frye standard originates from a 1923 case, Frye v. United States, where the court ruled that, to be admissible, scientific evidence must be “sufficiently established to have gained general acceptance in the particular field in which it belongs.”3

The Daubert standard is more recent, derived from the 1993 case Daubert v. Merrell Dow Pharmaceuticals, where the Supreme Court went beyond Frye to say that evidence must have sufficient scientific validity and reliability to be admitted as relevant “scientific knowledge” that would “assist the trier of fact.”4

Challenges to Admissibility

People of New York v. Castro was a landmark murder case commonly cited as the first serious challenge to the admissibility of DNA evidence. During the pre-trial hearing in the New York Supreme Court, DNA evidence from a bloodstain on the defendant’s watch was in question. The court determined that DNA identification theory, practice, and techniques are generally accepted among the scientific community, and that pre-trial hearings were required to determine whether the testing laboratory’s methodology was in alignment with scientific standards and produced reliable results for jury consideration.

However, the testing laboratory’s procedures were called into question and expert testimony revealed that the lab had failed to use generally accepted, reliable techniques that could prove the blood on the watch was that of the victim. Interestingly, the Court did allow the DNA tests that ruled out the blood as that of Castro – upholding the DNA tests for exclusion but not inclusion since the process for determining a match is more complex than ruling out a match.

Because of its exhaustive process attempting to analyze the admissibility of this DNA evidence, in its opinion the New York Supreme Court outlined recommendations and requirements for future discovery phase proceedings, including the provision of copies of all laboratory results and reports to the court and defense, explanation of statistical probability calculations, explanations for any observed defects or laboratory errors, and chain of custody of documents.