It’s a Match: How Officials Used DNA to Identify bin Laden

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The Obama Administration used several methods, including DNA testing, to confirm that U.S. Navy Seals did in fact kill Osama bin Laden in a weekend raid in Pakistan, U.S. officials said on Monday.

In addition to facial-recognition techniques, analysis of photos by the CIA and confirmation from people at the site of the raid ­(quoting a senior U.S. defense official, CNN reported that “one of bin Laden’s own wives identified his body to U.S. forces, after the team made visual identification themselves”), DNA from the body was matched to confirm bin Laden’s identity.

(More on TIME.com: See pictures of a bin Laden family album.)

Matched to what? The U.S. is believed to have collected DNA samples from several of bin Laden’s family members during the decade since the terrorist attacks of 9/11. According to an ABC News affiliate in Boston, one of those samples belonged to bin Laden’s sister, who died of brain cancer about a year ago at Massachusetts General Hospital; after her death, government officials were reported to have taken some of her brain tissue for genetic testing.

DNA matching suggests with 99.9% certainty, officials said, that the man killed by a shot to the head in a compound in Abbottabad, a town about 75 miles north of Islamabad, was Osama bin Laden. That may be the best confirmation we’ll get, considering that the body has already been buried at sea in accordance with Muslim custom, which requires interment within 24 hours of death. The AP reported that Administration officials were “weighing the merit and appropriateness of releasing a photo of bin Laden.”

(More on TIME.com: “Why Was bin Laden Buried at Sea So Quickly?”)

So how does DNA matching work? Unlike traditional DNA sequencing, which is the lengthy and expensive process of mapping each of the hundreds of millions of nucleotides in your entire genome, DNA matching homes in on the small fraction of genetic markers that make you unique (99.9% of your DNA sequence looks like everyone else’s).

In a typical case, like, say, involving a crime, a test sample of DNA from the crime scene would be compared with a reference sample already on file from the suspect to see if they matched. In bin Laden’s case, presumably there was no reference sample from the man himself.

(More on TIME.com: “Celebrating the Death of Osama bin Laden”)

That’s where his brothers and sisters come in. Bits of a person’s unique genetic fingerprint are shared with his or her siblings and parents — since the latter are the ones who give you your DNA to begin with — so DNA swabs collected from the raid in Pakistan would have been matched with reference samples from bin Laden’s siblings. A close match identifies bin Laden with an exceedingly high probability of accuracy.

Indeed, taken together, the proof was strong enough to prompt President Obama to deliver a dramatic address to the nation on Sunday night declaring that the U.S. had successfully killed the terrorist mastermind.

(More on TIME.com: “Death Comes for the Master Terrorist: Osama bin Laden, 1957-2011″)

The identification was also confirmed with terrific speed. As Kit Eaton at Fast Company reported:

Typical lab-based DNA matching tests like this can take up to 14 days; they’re painstaking and need to be repeated several times to ensure the sample’s not contaminated from any other DNA sources. But that’s not necessarily the only way to do these tests: late in 2010, a University of Arizona team presented research on a machine that can do the analysis in just two hours in a largely automated way. It’s possible that knowing they were engaged on a mission to capture bin Laden, U.S. forces arranged for access to a machine like this to be on quick alert — probably for flying blood, cheek cells, and other samples taken from the body to the lab for expedited analysis.

Eaton also pointed out that DNA matching isn’t an exact science and that sibling matching is even less exact: “It all comes down to a probability, with a statement like, ‘There’s a 1 in 1 quadrillion chance this isn’t the same person in both DNA samples.’ In other words: conspiracy theorists still have something to talk about.”

‘Operation Get bin Laden’: Inside the Navy Seals’ Daring Raid.

Killer Betrayed by a Low-Tech Lair.

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