DNA as a Sketch Artist:
How Forensic Science Benefits
from Physical Predictions
By Katrina Voss
It’s a typical summer day in southwest Louisiana. The air is spongy with heat as alligators sun themselves lazily
along the lakes and bayous of Lake Charles. But, the city was a frightening place to be a woman from late 2002
through the summer of 2003. Five bodies had been found raped, murdered and dumped in the swamps between
Lafayette and Baton Rouge.
DNA had revealed just two relevant details at this point: the same man committed all of these crimes, and
his genetic profile had not been entered into the nationwide Combined DNA Index System (CODIS) database.
(CODIS is a U.S. database of the DNA profiles of offenders in closed cases, unsolved crimes and missing persons.)
Eyewitness accounts of a white man driving a pickup truck, as well as an FBI psychological profile, prompted police
to focus their investigation on leads involving only white men.
Based on these leads, police began an exhaustive effort to collect the DNA of a considerable number of
suspects, a process commonly referred to as DNA drag netting. By some reports, Louisiana police collected and
tested DNA samples from between 700 and 1,200 white men who seemed to fit the profile.
Enter Forensic Ancestry Testing
In the year the crime wave began, genetic ancestry testing had become popular among genealogists as a means
to explore their own family lineages. Having received the somewhat disparaging label, “recreational genomics,”
genetic ancestry testing in a forensic context was still a novel, and controversial, idea. However, confident that
a new approach to DNA testing might help the search, Louisiana detectives decided to try a direct-to-consumer
genetic ancestry test called AncestryByDNA.1
Geneticist, Mark Shriver, who worked on the case, explained that the test used a panel of ancestry-informa-tive genetic markers (AIMs) to infer genetic heritage from four “parental” populations: West African, European,
East Asian and Indigenous American. This four-population model is by no means applicable globally, although
it is particularly useful in the U.S. where the genetic ancestry of many residents is derived from just one or some
combination of these parental groups. 2 For example, Hispanics and Native Americans usually show significant
Indigenous American genetic ancestry.
Indeed, for Louisiana detectives, genetic ancestry testing helped provide a suspect description. Contrary to the
police profile, the AncestryByDNA estimate revealed that the perpetrator’s genetic ancestry was largely West African, suggesting that the he would likely be considered a black man, according to current U.S. conceptions of race.
Eyewitness accounts and the FBI physiological profile that described a white man were proven wrong.
Criminal Convictions from Ancestry Testing
With a major change in focus to their investigation, detectives followed up on a tip they had received months
earlier regarding a black man, Derrick Todd Lee. They obtained a voluntary sample from Lee, and used other
genetic markers known as short tandem repeats (STRs) to compare his DNA to that left on the victims.
Unlike AIMs, STRs generally do not provide information regarding ancestry or physical traits. Instead, STRs
are highly variable genetic markers used in CODIS as a sort of genetic barcode to identify individuals. Lee’s STR
profiles matched those from the DNA found on the victims, and on May 28, 2003, police arrested him. He was
convicted the following year of two of the Louisiana murders.