DNA samples from family members of Osama bin Laden were used to positively identify his body with “99.9 percent” certainty, the U.S. government has claimed.

How can the government be so certain? Modern forensic techniques analyze short tandem repeats: pieces of DNA that are copied different numbers of times in different individuals on the chromosomes that contain an individual’s genetic code.

Polymerase chain reaction and genetic sequencing can be used to count the number of tandem repeats in a genome.  The tandem repeat profile can then be compared between two individuals to find out whether their DNA profiles match.

Chad Nusbaum of the Broad Institute of MIT and Harvard in Cambridge, Mass., estimates that this process would take five or six hours, or even faster in a lab using proprietary technology dedicated to forensic identification.

This would have given military analysts time to perform a DNA analysis after the U.S. raid on Monday morning (May 2) in Pakistan, and deliver results to President Obama by the time of his announcement on Sunday night (May 1) in Washington, DC.

Samples also could have been collected from any of bin Laden’s living siblings or children, either with or without their knowledge, by obtaining discarded material bearing their DNA, such as beverage cups or dental floss. The strength of a match made between bin Laden’s putative DNA and that of his relatives would depend on how many related DNA samples are available for comparison, and how closely they are related to bin Laden.

Short tandem repeat analysis could be conducted on the y-chromosome, which is passed down from father to son. Such an analysis could be used to link the putative bin Laden to any of his known half-brothers or sons, further strengthening the evidence that it was indeed he who was killed in the Navy raid in Pakistan.

If it is true that bin Laden was the only son born to his mother and father, a combination of y chromosome and mitochondrial DNA markers could yield a strong match to bin Laden himself, because none of his half-brothers would have inherited the same combination of y chromosome and mitochondrial DNA markers that he has.

Short tandem repeat analysis could also have been conducted on nuclear chromosomal DNA from many bin Laden siblings and children, further cementing the case.