In the days since our first blog post about the Osama bin Laden DNA identification, we've seen plenty of questions--and a little new information--on how the match was performed. We rounded up the latest news on the science behind the identification and got some expert insight from Robin Cotton, Associate Professor and Director of the Biomedical Forensic Sciences Program at Boston University.

  • Where was the lab work done? We don't know exactly, but Cotton points out that it is not at all unusual for DNA analysts and other forensic scientists to be working in Afghanistan and Iraq. For instance, this want ad for a "DNA Analyst wishing to be apart of a dynamic team to work in deployed forensic laboratories in Iraq and/or Afghanistan" was posted to the American Academy of Forensic Sciences job board just last month. A quick look at the preferred skills for the job--"Experience with the following: ABI 3130xl (or 3100), Identifiler, Yfiler, and/or Minifiler chemistries, ABI 7500 (or 7000), ABI GeneMapper ID software, and/or the EZ 1 robot"--suggests some of the equipment that could have been used in this case.

    Contrary to the television-CSI-induced assumption that DNA matches require enormous, gleaming laboratories, said Cotton, the Bin Laden DNA identification could have been performed in a mobile lab unit about the size of a trailer. "The equipment that you see doesn't take up a lot of space, it doesn't require extraordinary kinds of electrical power," said Cotton. "It requires a clean place--you couldn't do it outdoors in the sand--but it wouldn't be hard to have what you needed," provided it "has the physical design to prevent contamination."

  • Bin Laden's half-sister's brain? Everyone from the New York Times to yours truly has called up Massachusetts General Hospital hoping for a confirmation of the report, first carried on ABC News, that an MGH-held DNA sample from Obama Bin Laden's half-sister's brain had been used to clinch the DNA match. However, the hospital was not able to confirm the story, saying in a statement that its "policy is to not release patient information to law enforcement agencies without a subpoena or similar order, and that after a reasonable inquiry it could find no indication that it had received a subpoena regarding DNA for a relative of Osama bin Laden.''

  • So whose DNA did they use? We don't know exactly, though officials have said that the analysis involved samples from multiple different relatives. The more, the better, explained Cotton--especially if the samples came from half-siblings. Scientists expect full siblings to share, on average, 50% of their short tandem repeats (STR), sequences of "junk DNA" that are a standard for forensic identification, though the match for a particular STR region could be zero, half, or 100%. Things get murkier with half-siblings. "You would have to have a collection of half-siblings" to make a solid identification, said Cotton. In the case of half-brothers who shared a father, explained Cotton, researchers could also use Y-chromosome analysis. But the "virtually 100-percent" confidence level claimed by the government would be difficult to obtain using half-siblings alone. A sample from one of Bin Laden's children, some of whom are believed to have been in the Abbottabad compound when Bin Laden was killed, could produce a match at a higher confidence level. But, added Cotton, until officials tell us more about the sources of the samples, we can only guess at precisely how they arrived at the match.

  • It's not all about DNA By examining photos of the body believed to be Bin Laden's against existing Bin Laden photos, intelligence officials said, they "were able to determine with 95-percent certainty that the body was Osama bin Laden." We don't know exactly how the match was made (you're probably getting used to hearing that by now) but Spencer Ackerman at Wired's Danger Room speculated that a handheld biometric device called the SEEK (Secure Electronic Enrollment Kit) II could have done the job. According to Ackerman, the four-pound device "takes iris scans, fingerprints and facial scans and ports them back to an FBI database in West Virginia in seconds." The SEEK II can "talk" to the FBI database wirelessly or by linking up with a local computer, and it can also be preloaded with its own on-board biometric database.

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