Fergie's Tech Blog

The Dilemma of 'CODIS Creep' - Genetic Surveillance for All?

Jeffrey Rosen writes on Slate.com:

In March 2003, a drunk in southern England threw a brick off a bridge late at night, striking and killing a truck driver traveling along the freeway below. Armed with DNA from the blood on the brick, the British police searched the United Kingdom's national DNA database, which includes convicted felons and people who have been arrested, but failed to get a direct match. They then conducted a DNA dragnet, asking hundreds of young men in the area to donate a sample voluntarily, but still came up short. Without any other leads, the police decided to conduct what's called a "familial search" of the national DNA database. They were looking not for perfect matches to convicted offenders but for near matches, in the hope of using them to identify a relative who might have committed the crime.

Ordinarily, when searching for actual offenders, the British police look for a perfect match to a DNA profile that contains 10 pairs of peaks, or "alleles," with one number in each pair provided by the father and the other by the mother. Only identical twins share genetic profiles on all 20 alleles, so if you get a perfect match between the DNA you find at the scene and the DNA database profile, you have very strong evidence that the person in the database committed the crime. But the police can also program the search to look for partial matches, identifying profiles that are similar but not identical to those in the database. A partial match can suggest that the person in the database didn't commit the crime, but a close relative whose DNA pattern varies slightly on some of the 20 alleles may have done so. Accordingly, the British authorities programmed the search to pull up any offender in the database who matched at least 11 alleles out of 20 from the blood on the brick.

Initially, this familial search produced more matches than the police could follow up. But then the authorities limited the search to young men from two counties near the crime scene. This narrowed the number of partial matches to around 25. After interviewing the person whose profile represented the closest match—16 out of 20 alleles—the police found he had a brother who lived in one of the nearby counties. They went to the brother, Craig Harman, who agreed to give a DNA sample. It turned out to match the DNA on the brick. Harmon confessed after being confronted with the match, and in 2004, he was convicted of manslaughter.

posted by Fergie @ 3/20/2009 04:50:00 PM