Mehsud is described by U.S. experts as a homegrown Pakistani militant who operates from the remote tribal lands along the Afghanistan-Pakistan border. He has had contacts with both the Taliban movement and with elements of the fugitive Al Qaeda high command—whose leaders, Osama bin Laden and Ayman al-Zawahiri, are believed to be hiding out in the same region. A U.S. official said that Mehsud has been linked to previous suicide bombings, though the official could not cite any particular incidents in which his involvement had been established.

U.S. officials dismiss assertions by Bhutto supporters that Musharraf or his inner circle somehow orchestrated the attack on the opposition leader. They believe that Musharraf hoped that a political deal with Bhutto, brokered by the United States, would help him bolster his popularity. Yet some U.S. and U.K. officials say there may be some validity to complaints from Bhutto's camp that the government security meant to protect her was woefully inadequate.

But the officials say Bhutto herself may not have been entirely blameless for the lapses. For example, two current and former U.S. officials said that Pakistani authorities had advised Bhutto to travel by air rather than ground convoy and had even offered her official helicopter transport. But she turned down such assistance, according to these accounts, saying that she wanted to be close to her supporters. Rawalpindi, the city where she was assassinated, is a military garrison town where Musharraf himself has survived assassination attempts. Yet Bhutto drove into a crowd and then stuck her head out of her armored vehicle's sunroof, making it difficult for guards to protect her from a determined killer.

Significantly, Pakistan's call for outside help did not include the FBI—an absence that appears noteworthy, given the normally close working relationship between Pakistani security forces and the bureau. British and American counterterrorism officials said one reason that the Pakistanis may have chosen Scotland Yard over the FBI is that Islamabad fears that conspicuous U.S. involvement in the inquiry could escalate violent protests against Musharraf for being too close to Washington.

Terror Watch appears weekly on Newsweek.com

© 2008