In the past ten years we have seen great advances and a powerful criminal justice tool: deoxyribonucleic acid, otherwise known as DNA. DNA is being used by law enforcement to identify criminals with indisputable accuracy in cases where biological evidence exists. But, DNA can also be used to clear suspects and exonerate individuals who have been wrongfully convicted of crimes they didn’t commit.
We are constantly hearing new stories about how DNA has been used to solve crimes. For instance, in 1999, New York authorities were able to link a man through DNA evidence collected at the crime scene to at least 22 sexual assaults and robberies that had terrorized the community. In 2002, Philadelphia authorities and authorities in Fort Collins, Colorado, used DNA evidence to solve a series of rapes and murders perpetuated by the same individual.
In 2001, DNA evidence provided a major breakthrough in the “Green River” killings that had been unsolved for years despite the efforts of a large law enforcement task force and a $15 million dollar investigation.
How is DNA evidence used to solve crimes?
Generally speaking, DNA evidence is used to solve crimes in two ways. If a suspect has been identified, a sample of his DNA can be compared to evidence collected from the crime scene. The results from this DNA test can establish whether the person committed the crime or not.
If a suspect has not yet been identified, biological evidence from the crime scene can be analyzed and compared to offender profiles in various DNA databases used by law enforcement to help identify the perpetrator. Furthermore, DNA collected from the crime scene can be tested and linked to other crime scenes through DNA databases.
DNA databases play a key role in the testing and comparing of DNA evidence. In the late 1980s the federal government created a system called the Combined DNA Index System (CODIS), which maintains DNA profiles obtained under local, state and federal systems in a set of databases that are made available to law enforcement all across the nation for law enforcement purposes. CODIS can do the following:
- Compare crime scene evidence to DNA profiles obtained from convicted offenders.
- Link DNA evidence obtained from different crime scenes, and identify serial criminals.
In the late 1980s and early 1990s states passed laws requiring offenders who have been convicted of certain offenses to provide DNA samples and currently all 50 states and the federal government have laws that require that DNA evidence be collected in certain types of crimes.
While DNA is a powerful tool, the current state and federal DNA collection and analysis system needs improvement because so many crime labs are backlogged with unanalyzed DNA samples. Many crime labs are ill-equipped to handle the increasing number of DNA samples and evidence, thereby leading to significant delays in the administration of justice.