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.

While the late 1980s and early 90s saw a number of judicial challenges to the admissibility of DNA evidence, most important cases established the admissibility of DNA evidence, when properly collected and analyzed.5 Where inadmissibility was found, it was largely due to questions about the validity of techniques used to derive or interpret the DNA profile (such as population statistics), or about the reliability of the lab or technician performing the analysis.6,7

In one such case, the Supreme Court of Minnesota acknowledged the scientific acceptance of DNA testing, but stated that “admissibility of [DNA] test results in a particular case hinges on the laboratory's compliance with appropriate standards and controls.” 8 In this case, the laboratory’s protocol and methodological validation process were deemed insufficient and the evidence was dismissed.

Even though DNA testing would grow more ubiquitous in the criminal justice system over its first fifteen years in use, another wave of cases came with advancements in DNA testing technology. Specifically, the movement toward abandoning the original methodology, restriction length fragment polymorphisms (RLFP) using VNTR loci, in favor of polymerase chain reaction (PCR) and sequencing technology using short tandem repeats (STRs) gave defense lawyers another opportunity to challenge the admissibility of DNA evidence by calling into question the new methodology’s reliability for determining DNA identification.

These issues were, for the most part, resolved in a string of cases around the year 2001 where courts repeatedly supported the method as reliable and accepted, with some recommending that the technique in general should no longer be the subject of judicial scrutiny,9,10,11 even in one Colorado case where the DNA evidence was initially found inadmissible based on questions about the DNA testing kit’s validation, but on appeal ruled generally accepted and admissible.12

The Emergence of DNA Databases

In addition to important court cases scrutinizing the reliability of DNA evidence upon review of laboratory methodology and validation processes, the introduction of the Federal Bureau of Investigation’s (FBI) Combined DNA Index System (CODIS) forensic DNA database – mandated by the federal DNA Identification Act of 1994, provided another set of pressures on forensic laboratories to ensure their methodologies were sound and validated.

All DNA laboratories that are federally operated, receive federal funds, or employ software prepared for the CODIS are required to demonstrate compliance with the standards issued by the FBI. (Note: For a description of these and other standards that have governed DNA testing laboratories, see our earlier article from this series “Evolution of the Quality Assurance Documents for DNA Laboratories” Forensic Magazine, February/March 2005.)

Similarly, the Violent Crime Control and Law Enforcement Act, implemented in 1994 advocated for uniform standards to be used for forensic DNA testing. It further provided federal support for state and local law enforcement agencies to improve their DNA testing capabilities.

Development of All Felons Databases

In addition to CODIS, all 50 states maintain DNA databases. The types of profiles that are included vary from state to state, with a general trend toward expanding the crimes justifying inclusion. In 1990, Virginia became the first state to enact an all felons’ law that required DNA from anyone convicted of a felony. Most states at that time included only certain offenses, such as sexual assault. By 1999, six states had All Felons databases and today there are 38 states with this legislation; the majority of the remaining states have some legislation in review to expand their DNA databases to include all felons.

The expansion of DNA databases has led to a growing number of “cold hit” cases, where no suspect has been identified, but samples from a crime scene submitted to the local, state or federal DNA database result in a match from a previously convicted offender. In 2002, Virginia became the first state to execute a criminal convicted of murder and rape based on a “cold-hit.” As testimony to the importance of DNA databases, the convicted felon, James Earl Patterson, was already serving time for a rape and was scheduled to be released in 2004.

Emergence of “John Doe” Warrants

In addition to facilitating “cold hits,” DNA database legislation has given rise to a new type of arrest warrant – termed “John Doe” or “DNA” warrants because the warrant is issued not for a named person, but for a genetic code identified as part of a criminal investigation for which no suspect has been identified and no database match has yet been found. In September of 1999, a district attorney in Wisconsin became one of the first prosecutors to obtain a warrant and file criminal charges against a man identified in the warrant solely by his DNA profile. The primary purpose of these warrants is to toll the statute of limitations in cases of violent crimes. Many states have sucessfully convicted offenders based on John Doe warrants and several, such as Wisconsin, have passed legislation legallizing their use.

Post Conviction DNA testing

Just as recent legislation has supported the increased use of DNA for prosecution, legislation to protect the falsely convicted has also been gaining ground in recent years. Since 1989, more than 150 people imprisoned in the United States have been proven innocent through post-conviction DNA testing. The Innocence Project was established in 1992 to support the rights of convicted felons who maintain their innocence and has been a driving force in supporting legislation in this area, and most states have since passed special statutory provisions for post-conviction DNA testing.

Justice for All

On October 30, 2004, President George Bush signed the Justice for All Act, which significantly enhanced funding and guidelines for the use of DNA technology in the judicial process. Among other things, the Act strengthened the rights for convicted felons to obtain post-conviction DNA testing if they assert their innocence and that the DNA testing would produce new evidence in support of that innocence, and the DNA testing would create a reasonable probability that the applicant did not commit the offense.

In addition, the law authorizes additional grants to states and local governments to analyze DNA samples and improve DNA labs. It promotes quality assurance in DNA testing by requiring government labs to undergo accreditation and auditing at least once every two years to prove compliance with federal standards. Under the law, CODIS is expanded to allow state crime labs to include the DNA profiles of all individuals whose DNA samples were lawfully collected, including samples from arrestees and juveniles adjudicated delinquent. The law also extends the statute of limitations at the federal level in cases where DNA testing implicates a perpetrator until the time that perpetrator’s actual identity is discovered.


The utility and power of DNA as a tool to convict criminals or exonerate suspects has been greatly supported by the careful legal reviews and stringent quality assurance guidelines that have been developed over the course of nearly twenty years.

The ongoing legislative and judicial reviews at state and federal levels has contributed significantly to the evolution of DNA analyses and played an important role in its rapid adoption as a legal tool. This careful scrutiny has also made DNA analysis one of the most robust and powerful tools used today in the criminal justice system.

As the technology continues to advance, judicial and legislative reviews should continue to ensure that DNA analysis serves justice and protects the public.


1) Andrews v. State, 533 So. 2d 841 (Fla. Dist. Ct. App. 1988)
2) State v. Woodall 385 S.E.2d 253 (W. Va. 1989)
3) Frye v. United States, 293 F. 1013 (D.C. Cir. 1923)
4) Daubert v. Merrell Dow Pharmaceuticals, 113 2786 (S.Ct. 1993)
5) United States v. Yee , 134 F.R.D. 161, 208 (N.D. Ohio 1991)
6) Commonwealth v. Curnin, 409 218, 565 N.E.2d 440 (Mass.1991)
7) State v. Bible, 858 P.2d 1152 (Ariz. 1993)
8) State v. Schwartz, 447 N.W.2d 422, 428 (Minn. 1989)
9) People v. Hill, 107 Cal. Rptr. 2d 110, 89 Cal. App. 4th 48, 59-60 (Calif. 2001)
10) Lemour v. State, 802 So. 2d 402 (Fla. Dist. Ct. App. 2001)
11) State v. Butterfield, 27 P.3d 1133, 1144 (Utah 2001)
12) People v. Schreck, 22 P.3d 68, 81 (Col. 2001)

Karen Cormier is Associate Product Manager at Applied Biosystems. She can be reached at
Lisa Calandro is Senior Forensic Scientist at Applied Biosystems. She can be reached at
Dennis Reeder is Senior Scientist, Validation Group at Applied Biosystems. He can be reached at
Applied Biosystems, 850 Lincoln Centre Drive, Foster City, CA 94404; 800-327-3002;