How forensics experts use DNA to create "mugshots" of a criminal's faceS

What if forensics experts could use a microscopic sample of DNA to figure out what a criminal suspect looks like? No, it's not science fiction. In just a few years, investigators may be reconstructing suspects' faces from DNA.

Finding out what a criminal looks like is a crucial step in any investigation. Surveillance images or composite sketches based on witness' accounts put the perpetrator's face in the public eye, and make it a lot harder to escape justice. There's a problem though – often, no one sees what the criminal looks like. Even if they do, humans are notoriously bad at making detailed observations during traumatic events, so eyewitness accounts can be wildly inaccurate.

Criminals might leave something else behind, however: a tuft of hair, a few drops of blood, some saliva on a cigarette butt. Any of these can be used to isolate and profile the suspect's DNA. But with no one to match the DNA to, you still have no idea who the suspect is or what he or she looks like. That might change in the near future.

What does your DNA reveal about your face?

Your DNA determines a lot about you, including many of your physical characteristics. Eye color and hair color are obvious examples, but DNA can also be used to trace your ancestry to a general region, which might offer other clues about your appearance. That was the method used by researchers from the University of Copenhagen, who sequenced the DNA of a 5,000-year-old Eskimo. A bit of the Saqqaq tribesman's hair was found in ice in 1986, then forgotten until being rediscovered by the DNA team a few years ago.

The DNA revealed that the subject was closely related to northern Asian ancestral groups, and based on this information, they were able to examine certain gene sequences and find a probable appearance for a prehistoric man they'd never seen (artist's conception, pictured above). They noted that he had dark skin and hair, brown eyes, and probably a stocky build, along with a tendency toward male pattern baldness (oddly, major media outlets seemed to think the baldness part was the most interesting aspect of this story). They even typed his blood (A+) and determined that he would have been vulnerable to alcohol addiction.

Identifying criminals

Will that method work with a modern human, using DNA evidence left at a crime scene? It's a much more difficult process, although several companies and research teams are working on it. One problem is that humans travel and breed with people far outside their regional ancestral groups today. Tracing a suspect's DNA to northern Europe, for example, won't tell us much about a suspect's appearance if his mother happens to be Korean.

DNA also can't account for environmental factors that can drastically affect someone's appearance. A criminal that grew up in an impoverished country might be much shorter and slighter than predicted due to childhood malnutrition. Plus, there are lots of ways to change appearance at will: dye your hair, wear colored contacts or grow a beard.

Still, there is some morphological information to be pried from DNA. By examining telomeres (chromosomal parts that show age wear), forensic experts can make educated guesses about a subject's age, although high levels of physical fitness can skew the results. Other genetic markers can reveal a host of probable physical attributes.

The ethical issues

It turns out the real barrier to DNA mug shots might be more ethical than technological. As early as 1997, the DNA Advisory Board chose to omit genetic markers tied to geographic ancestry from the official set used for evidence matching because they feared it would be politically controversial. With the practice as imprecise as it is, there are fears that it would lead to unfair racial profiling or wrongful convictions.

Forensic investigators believe DNA appearance profiles could be used as a supplemental tool to help focus investigations that don't have any leads. In fact, it was used this way in the hunt for the Baton Rouge Serial Killer in 2002. Witness reports placed a white man at the scene, but an analysis of DNA left at one of the crime scenes showed the suspect was likely black. Derrick Todd Lee was eventually arrested and convicted of the crimes, and though the DNA profile was not directly used to capture him, it turned out to be correct.

Sources:

"DNA and a New Kind of Racial Profiling." Popular Science, Dec. 2003.

"DNA Secrets of the Ice Hair." Nature.

"Portrait in DNA: Can forensic analysis yield police-style sketches of suspects?" Scientific American, May 2010.