Achieving a satisfactory identification of the world's most wanted man is not, it turns out, a simple matter. According to the US government, the body of Osama bin Laden, killed during a raid on a compound in Abbottabad, Pakistan, on 2 May, was identified by comparison to photographs, confirmation from one of his wives at the compound, facial-recognition software, and – the gold standard for identification – DNA analysis.
John Brennan, Assistant to the President for Homeland Security and Counterterrorism, said the DNA evidence provided a match with "99.9 per cent confidence". That would require the comparison of DNA from the body with that of people known to be related to bin Laden. Bin Laden had no full siblings, but more than 50 half-siblings and up to 24 children.
Using DNA from many half-siblings could produce a DNA match of greater than 90 per cent confidence, but it would be difficult to get as high as 99.9 per cent without a closer relative says Rhonda Roby, a forensic geneticist at the University of North Texas Health Science Center, Fort Worth. Roby, who led the team using DNA evidence to identify the remains of people killed in the 9/11 attacks in 2001, says that the statistical analysis based on DNA from half-siblings is more complex and less reliable than analysis based on DNA from a closer relative like a parent or child.
Reports indicate that one of bin Laden's sons was also killed in the raid, possibly 20-year-old Hamza bin Laden. Roby says DNA from a son and several half-siblings could confirm Osama's identity with 99.9 per cent accuracy.
Full paternity trio?
If, however, the government was able to obtain DNA from bin Laden's body, his son and also that son's biological mother – who might have been at the compound during the raid, it could perform DNA profiling with a "full paternity trio", assuring 99.9 per cent accuracy, Roby says.
The provenance of the DNA used in the comparison is unknown, as is the nature of the test itself. However, it is likely that forensic scientists analysing bin Laden's DNA used the polymerase chain reaction to amplify between 13 and 16 key regions called short tandem repeats (STRs), then compared the pattern of these with the same STRs from that of his relatives.
The agency responsible for conducting the analysis is also unconfirmed: media reports have named both FBI and the CIA. Several sources suggested that DNA was subpoenaed from the body of a half-sister of bin Laden, when she reportedly died at Massachusetts General Hospital in Boston, but the hospital was unable to confirm the report. "There is no evidence she was even here," says spokesperson Sue McGreevey.
FBI special agent Greg Comcowich would not confirm or deny any investigative steps the FBI has taken. When asked whether the agency would release any further information on the DNA analysis, he replied: "Not that I'm aware of."