The History of DNA Testing in Criminal Investigations

The DNA double helix

DNA testing has revolutionized the way the criminal justice system investigates crime. No other forensic tool enjoys the level of confidence that DNA inspires for justice officials and juries. When a suspect's DNA matches samples from a crime scene---or a DNA databank---it virtually guarantees a conviction. DNA testing also has proven innocence. The history of DNA in criminal investigations reveals a profile unmatched by any other forensic technology.

Historic Discoveries

According to Nature Education, Friedrich Miescher identified in 1869 what scientists later called DNA "inside the nuclei of human white blood cells," a discovery that scientists built upon until Watson and Crick modeled the double helix structure in the 1950s. The key discovery for criminal investigations did not come until 1984, however, when Sir Alex Jeffreys identified what he named "genetic fingerprints," according to the University of Leicester. It marked the first time scientists could differentiate individual DNA.

Function

Judges will throw down the gavel if tests fail admissibility standards.

DNA testing uses only a small fraction of a person's genetic code. Genetic fingerprints rely on "minisatellites," described by the University of Leicester as "short sequences of chemical building blocks" with variations "unique to each person". Narrowing the focus even further, genetic profiling---the kind of testing appropriate for criminal investigations---examines only one minisatellite at a time, says the University of Leicester. Although different methods have become standard practice, tests must meet admissibility standards for evidence in U.S. criminal trials, according to the Committee on DNA Technology in Forensic Science.

Early Criminal Applications

DNA can lock someone in jail or set him free.

The first criminal justice application proved a confessed murderer innocent. According to a 1996 National Institute of Justice report, a suspect in the 1986 rape-murder of two girls in Leicester, England, confessed to only one murder. In an attempt to prove the suspect killed both girls, police contacted Sir Alex Jeffreys, asking him to match the suspect's DNA to genetic material from the crime scene. They did not match, and police later arrested another man. The first conviction based on DNA evidence came in the 1987 rape trial of Tommy Lee Andrews in Orange County, Florida.

Beyond Human DNA

DNA from HIV injected through a syringe helped convict one doctor.

DNA testing has moved beyond humans. According to a 2001 newsletter by the American Prosecutors Research Institute, prosecutors used the DNA profile of Palo Verde tree seedpods found in a murder suspect's truck bed to place him at the murder scene. In another case described by the American Prosecutors Research Institute, the DNA profile of an HIV strain helped convict a doctor accused of injecting his ex-lover with the virus.

DNA Databanks

Police can use "John Doe" arrest warrants to handcuff an offender.

In 1990, the Federal Bureau of Investigation created the Combined DNA Index System (CODIS), which according to the bureau "generates investigative leads" by storing DNA profiles from crime scenes, convicted offenders and arrestees in a searchable databank . Databank searches help resolve cold cases or link crimes to a single offender. According to Forensic Magazine, they also have led to "John Doe" arrest warrants, issued for unidentified genetic code instead of a person, sidestepping any statute of limitations . Once law enforcement gets a databank hit, officials arrest the owner of the DNA.

References

• Scitable by Nature Education: Discovery of DNA Double Helix Watson and Crick
• University of Leicester: Genetic Fingerprinting Explained
• National Institute of Justice: Convicted by Juries, Exonerated by Science: Case Studies in the Use of DNA Evidence to Establish Innocence After Trial
• Forensic Magazine: Evolution of DNA Evidence for Crime Solving - A Judicial and Legislative History
• American Prosecutors Research Institute: Silent Witness Newsletter 2001

Resources

• Human Genome Project Information: DNA Forensics