New techniques employed by DNAPrint Genomics, such as DNAWitness, have served to increase DNA's utility in criminal investigations.
Scientists are continually increasing the number of markers available for analysis. DNA is made up of a string of four letters that spells out the blueprint for an organism. A short tandem repeat marker (STR) is a block of these letters repeating a number of times at a given location. A single nucleotide polymorphism (SNP), in contrast, is a change at a single letter of the code at a given location where one letter is swapped for another.
"Originally DNAWitness (the lab's ancestry process) utilized only 71 SNP markers; currently we use 176," notes Thomas. "By adding other powerful ancestry informative SNP markers, our analysis is more refined and robust. We have observed trends in groups of people from around the world, and we can supply that information to an investigation."What is ancestry DNA?
Ancestry DNA analysis determines the bio-geographical ancestry (BGA) of a sample. It paints a picture of the relative incidence of the four major population groups — European, East Asian, Native American and Sub-Saharan African — in a given DNA sample. A person with 95-percent European ancestry is expected to be Caucasian and not Sub-Saharan African or Asian.
There are three specific areas where having ancestry information from DNA can assist investigators. It can:
- identify the physical characteristics of an unknown suspect,
- identify an unknown victim, and
- narrow the pool of "persons of interest."
Ancestry DNA analysis has already been successfully demonstrated. Consider the following cases:
In 2002 and 2003, the Lafayette Parish (Louisiana) Sheriff's Office investigated the murders of six victims linked to a single assailant near Baton Rouge and other locations in southern Louisiana. The DNA left behind at all the crime scenes matched, but there were conflicting eyewitness reports. As a result of combining standard and ancestry DNA analysis, Derrick Todd Lee was convicted in 2004.
In the small community of Mammoth Lakes, California, a hiker and his dog found a human skull near a campground in 2003. Forensic anthropologists first thought the victim might be Asian because of her size. Using ancestry DNA technology, she was found to be 100 percent Native American.
Meanwhile, investigators in London for 16 years have been investigating a series of rapes, which initially included more than 24,000 people of interest. Collecting DNA from such a large group was controversial and required significant resources. This time, using ancestry DNA technology, investigators pinpointed the probable origin of the rapist and narrowed the field of suspects considerably.Identify physical characteristics
In the Louisiana case, the state's Multi-Agency Homicide Task Force initially had relied on eyewitness testimony to develop a "Caucasian" description for the person of interest. DNAPrint Genomics processed the DNA evidence and determined the suspect was 85-percent Sub-Saharan African and 15-percent Native American. Based upon those findings, the task force materially altered the focus of its investigation and included Lee as a person of interest.
Ray Wickenheiser, a forensic consultant in Irving, Texas, and former director of the Acadiana Criminalistics Laboratory in New Iberia, Louisiana, remembers the case's unique challenges.
"We used every technique at our disposal to help solve the case of the South Louisiana Serial Killer," he recalls. "The public was mobilized via the media. Every tip was evaluated and investigated. The killer left his DNA calling card at every crime scene, but no match was made. Thus, every friend and neighbor was a suspect."