This theory’s been floating around since at least 2006, when the FBI noticed that KSM’s hands bear a striking resemblance to the hands seen wielding the blade in the infamous video of Pearl being beheaded. So prominent was the hypothesis, in fact, that it drew a (skeptical) response from Pearl’s own father. The obvious evidentiary problem: How do you go about making a positive identification of a hand? Unless there’s a telltale scar, there’s no way to hurdle a standard of proof as high as “beyond a reasonable doubt.”

Or is there?

According to the new report, which was prepared by faculty members and students at Georgetown University, U.S. officials have concluded that vascular technology, or vein matching, shows that the hand of the unseen man who killed Pearl on video is that of Mohammed. The report also says Mohammed told the FBI that a senior al-Qaeda operative advised him to take control of Pearl from his original kidnappers.

The 31,000-word report, published in conjunction with the Center for Public Integrity at www.publicintegrity.org, is among the most complete and graphic accounts of Pearl’s death…

Mohammed slashed Pearl’s throat, killing him, but one of his accomplices failed to operate the video camera, which they had brought to capture the murder for propaganda purposes. Mohammed restaged the killing, this time decapitating Pearl, according to the report. He then dismembered Pearl’s body, and it was buried on the compound. Guards washed the bloody floor and then prayed, foreheads to the ground, on the same surface where their prisoner had just been killed, the report said.

The report said that 27 men, including guards and drivers, played a part in the kidnapping and murder, and that 14 remain free in Pakistan.

KSM told interrogators that he was encouraged via phone to take custody of Pearl and do the deed by Al Qaeda capo Saif al-Adel, who was allegedly under house arrest in Iran at the time and who was reported to have finally returned to the battlefield in Waziristan just last year. (How was al-Adel able to keep in touch with AQ operatives in the field while under “house arrest” unless Iran was enabling him?) The technology of “vein matching” seems straightforward — it follows the same principle of unique blood vessel patterns as retinal scanning — but whether the patterns in a hand are unique enough to stand up in court is so far unclear. Assuming Obama and Holder are willing to chance it, this is potentially a way to get an easy conviction against KSM in civilian court, which would solve their problem (in his case, at least) of holding a detainee indefinitely without trial. If he’s acquitted of Pearl’s murder, they can send him back to his pen at Gitmo on grounds that they need to hold him for an eventual 9/11 trial; if he’s convicted, then they can proceed to the 9/11 trial knowing that there’s already a murder conviction on the books in case the jury does something bizarre and acquits him. A conviction in the Pearl case is insurance, in other words, against the political fallout from a bad outcome in the 9/11 case.

Three looming problems, though. One: As noted above, vascular analysis isn’t established yet the way, say, DNA analysis is. If it’s the feds’ only hard evidence against him and either the jury is skeptical of it or the court deems it inadmissible, the case falls apart. Two: Pakistan’s already convicted Omar Sheikh for Pearl’s kidnapping and murder, a fact that would no doubt be hammered by KSM’s defense. And since many of the accomplices are still at large, corroborating testimony of KSM’s guilt will be hard to come by. Finally, three: While KSM has in fact confessed to Pearl’s murder — and might do so again if given a chance to grandstand in open court about jihad — the interrogation methods used to extract his confession will naturally become a centerpiece of the defense, turning the trial into precisely the sort of propaganda circus that opponents of civilian trials for detainees have warned about. Worth the risk? For Obama and Holder, I’m thinking … yeah, maybe.

The Time piece in 2006 that first fingered KSM as the culprit mentioned that the Bush administration wanted to try him for the murder, so these considerations have obviously been kicked around for awhile. Team Bush wanted to do it in a military commission, though, not in civilian court; then again, Team Bush didn’t have a vascular fingerprint “proving” whodunnit. And Team Bush didn’t have a base that’s unhappy with his Gitmo policy the way the left is with Obama’s. Putting KSM on trial in federal court for Pearl’s murder would be a convenient sop to progressives and a nice victory ahead of the 2012 election — assuming it ends in conviction, of course. If it doesn’t? Oh boy.