DNA evidence has transformed forensic science, offering a powerful method for solving crimes and identifying individuals. It allows investigators to link suspects to crime scenes, identify victims, and exonerate the wrongly accused. Its emergence has reshaped criminal justice systems, moving investigations beyond traditional methods to incorporate precise genetic matching.
The Genesis of DNA Fingerprinting
The scientific foundation for DNA evidence was laid in 1984 by Dr. Alec Jeffreys at the University of Leicester in the United Kingdom. Dr. Jeffreys discovered that sections of DNA contain repetitive sequences, known as minisatellites, which vary significantly among individuals. This variation creates a unique genetic pattern, leading to his concept of “DNA fingerprinting.”
The initial technique developed by Jeffreys was Restriction Fragment Length Polymorphism (RFLP) analysis. This method involved cutting DNA with specific enzymes and separating the fragments by size to create a unique pattern. RFLP had limitations; it required a relatively large amount of DNA and the sample needed to be undegraded. The process was also time-consuming.
First Cases and Legal Acceptance
The first real-world application of DNA fingerprinting in a criminal investigation occurred in the United Kingdom with the Colin Pitchfork case. In 1986, DNA evidence linked semen samples from two murders, Lynda Mann (1983) and Dawn Ashworth (1986), to a single perpetrator. The DNA evidence also exonerated an initial suspect, Richard Buckland, who had confessed to one of the murders.
A mass screening of over 5,000 local men followed, leading to the identification and conviction of Colin Pitchfork in 1987. He became the first person convicted of a crime based on DNA evidence. In the United States, the People v. Castro case in 1989 marked a significant moment for legal acceptance. While some DNA evidence in this murder case was deemed inadmissible due to laboratory procedural issues, the court generally accepted the underlying scientific theory of DNA identification. This case established an early precedent, highlighting the need for rigorous standards for DNA evidence in courtrooms.
Advancements in DNA Profiling
Following these initial breakthroughs, DNA technology evolved, making analysis more efficient and sensitive. A significant advancement was the Polymerase Chain Reaction (PCR) technique. PCR revolutionized DNA analysis by allowing scientists to amplify minute quantities of DNA, creating millions of copies from tiny or degraded samples. This overcame a major limitation of the earlier RFLP method.
The shift to Short Tandem Repeat (STR) analysis transformed forensic DNA profiling. STRs are shorter, repetitive DNA sequences. STR analysis is faster than RFLP, requires smaller samples, and is the basis of modern forensic DNA testing. The development of national DNA databases, such as CODIS in the U.S. and the National DNA Database in the UK, amplified the utility of DNA evidence. These databases allow law enforcement to compare DNA profiles from crime scenes against profiles of convicted offenders and arrestees, linking cases and identifying serial criminals.