Osama bin Laden aimed to assassinate President Barack Obama but directed fellow al-Qaida fighters to leave Vice President Joe Biden alone, describing him as "totally unprepared" to take over and predicting a "crisis" in America if that happened, according to a newly declassified letter from the terrorist mastermind.

In the missive, part of a trove of documents seized by Navy SEALs in the raid that killed bin Laden one year ago, bin Laden asks for an update on a plan to kill Obama or Gen. David Petraeus either in Pakistan or at Bagram Air Base in Afghanistan. (Obama made a televised speech from Bagram during his surprise visit to the war-torn country this week.)

Bin Laden detailed how he ordered one loyal follower to "prepare two groups—one in Pakistan and the other in the Bagram area of Afghanistan—with the mission of anticipating and spotting the visits of Obama or Petraeus to Afghanistan or Pakistan to target the aircraft of either one of them."

"They are not to target visits by US Vice President Biden, Secretary of Defense Gates, Joint Chiefs of Staff (Chairman) Mullen, or the Special Envoy to Pakistan and Afghanistan Holbrook (sic). The groups will remain on the lookout for Obama or Petraeus," the Saudi-born extremist wrote.

"The reason for concentrating on them is that Obama is the head of infidelity and killing him automatically will make Biden take over the presidency for the remainder of the term, as it is the norm over there. Biden is totally unprepared for that post, which will lead the US into a crisis. As for Petraeus, he is the man of the hour in this last year of the war, and killing him would alter the war's path. So please ask brother Ilyas to send to me the steps he has taken into that work," bin Laden continued.

The Combating Terrorism Center at West Point published a report analyzing the documents—as well as the documents themselves, in the original Arabic and in English translations—on its official website. In a note accompanying the letter, labeled "SOCOM-2012-0000019," the center's analysts described it as "a long letter authored by Usama bin Ladin after the death of Sheikh Sa'id (Mustafa Abu'l-Yazid) in late May 2010 and it is addressed to "Shaykh Mahmud" (`Atiyya) who he designates as Sa'id's successor."

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The 17 declassified documents include letters or draft letters, running 175 pages in Arabic and 197 in English. The CTC notes that getting a full picture of bin Laden's plans, or of al-Qaida's relationships, strategies and operations, is impossible to do from such a limited sample. The documents, carefully declassified by the Obama administration, reenforce some of the president's key messages, notably that al-Qaida has been struggling as American and allied forces kill key operatives, and as Muslims criticize the group for killing co-religionists.

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