The Pakistani government's contradictory statements about the assassination of opposition leader Benazir Bhutto have become so tangled that some U.S. and U.K. officials are now expressing serious doubts about Islamabad's official explanations. A senior Bush administration official told NEWSWEEK that there is considerable reason to be skeptical about virtually everything the Pakistanis have said about the circumstances of Bhutto's death. "I don't put much stock in their whole story," said the administration official, who, like others quoted in this article, asked not to be identified talking about sensitive diplomatic matters.

Scotland Yard announced Wednesday that it is sending a "small" team of counterterrorism investigators to assist in the investigation of the assassination at Pakistan's request. The invitation to Scotland Yard—a reversal of Islamabad's previous refusal to accept outside help—comes after damaging statements by Pakistani doctors to the news media suggesting that they had been pressured to alter their accounts about the cause of Bhutto's death. Some U.S. officials now believe that President Pervez Musharraf's government is attempting to cover up its own security forces' negligence in failing to provide adequate protection for Bhutto.

"The Pakistanis know very well how to protect people," the U.S. official said. Not only were the assassin and a suicide bomber able to penetrate an official Pakistani security detail, said the official, but Bhutto was attacked at the precise moment when her security guards should have been most on alert. "She's attacked at the moment she was most vulnerable," said the official. "Every security person knows you're most vulnerable when you're getting into and out of a car … This was negligence."

In a further indication of official doubts about Pakistan's version of events, Pennsylvania Sen. Arlen Specter—citing "the uncertainty" about who assassinated Bhutto—Wednesday called for United Nations Secretary General Ban Ki-moon to appoint a special investigating commission to probe the assassination. Specter, along with U.S. Rep. Patrick Kennedy, had been scheduled to meet with Bhutto the evening of her death—a session in which an associate of the former prime minister was planning to give the visiting U.S. lawmakers a report on alleged "prepoll rigging" by the Pakistani military's Inter-Services Intelligence directorate. Specter—who once served on the Warren Commission that investigated the John F. Kennedy assassination—added in a letter to the U.N. secretary general, "In a matter of this sort, it is to be expected, based on what happened following the assassination of President Kennedy, to have a wide range of allegations and conspiracy theories."

Pakistani spokesmen have blamed jihadists for the attack on Bhutto. Last week Musharraf's government released a purported intercept of a conversation in which an apparent terrorist operative was congratulated by an alleged Pakistani jihadist leader named Baitullah Mehsud for his operatives' role in carrying out the assassination. But Musharraf's administration then damaged its credibility by releasing contradictory statements about the details of how Bhutto died—claims that remain unresolved in part because her family buried her body without a postmortem examination. At first officials and Bhutto aides claimed that she had been shot; the government later claimed that she had died from a blow to the temple suffered when her head struck the sunroof of her car. Then television pictures surfaced showing a gunman firing several shots at her and her head apparently recoiling in response.

Another U.S. counterterrorism official said American experts are still unable to confirm the authenticity of the alleged intercepted conversation. Purported representatives of Mehsud have denied that he had any role in the attack. The U.S. official noted, however, that intelligence agencies have picked up some fresh "indications" that Mehsud played a role in the attack and that he was still very much regarded as a potential suspect.