In April 2018, law enforcement officials and forensic investigators in California announced the arrest of Joseph James DeAngelo Jr., a 72-year old man accused of 12 murders that took place between 1976 to 1986. With this arrest, the mystery of the Golden State Killer was solved thanks to the forensic analysis of deoxyribonucleic acid, a criminal justice technique that dates back to the mid-1980s.
In 1984, a genetics researcher at the University of Leicester in the United Kingdom developed a method to detect unique sequences that can identify an individual with biological accuracy. This DNA profiling method starts with the collection of human tissue or bodily fluids, which can be obtained with personal consent, by means of a court order or through investigative techniques such as crime scene evidence gathering. Around the same time, controversial American scientist Kary Mullis developed the polymerase chain reaction process of DNA analysis, which provides greater accuracy and the investigative advantage of being able to analyze very small and degraded samples such as saliva that may have been left on a discarded cigarette butt.
<strong>Early DNA Forensic Analysis</strong>
The first criminal case investigated with the assistance of DNA analysis took place not far from the birthplace of this genetic breakthrough. In 1986, two murder cases that included evidence of sexual assault were solved in the United Kingdom, specifically in Leicestershire. In this particular case, the DNA analysis was used to confirm a confession.
In the United States, the Federal Bureau of Investigation became interested in DNA analysis shortly after the first forensic database was established in the UK. By 1992, a kidnapping and sexual assault case in Vermont featured a decisive blood sample analysis that was allowed in court and upheld upon appeal. Two years prior to this case, a Florida appellate court also upheld the use of DNA in a criminal case.
<strong>DNA as Exonerating and Exculpatory Evidence</strong>
Even though DNA analysis is often associated with criminal investigations that lead to convictions, this forensic technique has also been used to overturn convictions and exonerate individuals who have been wrongly sentenced for crimes they did not commit.
In Virginia, the case of the “South Side Strangler” resulted in the execution of Timothy Wilson Spencer for a 1988 killing spree; however, it took DNA analysis to exonerate David Vasquez, a convicted man who had nothing to do with the crimes.
As of 2018, hundreds of individuals have been exonerated and released from prison thanks to investigations and forensic analyses argued in American courts. Legal scholars and scientists believe that U.S. courts may decide on thousands of DNA exoneration cases over the next two decades.