CIA Director Michael Hayden told the Washington Post that the former Pakistani prime minister was killed by fighters allied to Baitullah Mehsud. Mr Hayden did not reveal the sources for his claim. Apparently, CIA has come out with this conclusion based on their own independent intelligence sources and due diligence. With this CIA claim, there is now agreement between the Pakistani intelligence and the US intelligence on the identity of the people behind Benzair's assassination.
In fact, the CIA chief Hayden, goes further and believes it is part of a larger plan by combined Taleban-Al-Qaida forces to target Pakistani political leadership to destabilize Pakistan and take advantage of the ensuing chaos.
While there will continue to be alternative theories and claims of motives and conspiracies implicating Musharraf and PML(Q), there are reasons to believe that Taleban-Al-Qaida axis would want to eliminate Benazir from the scene. When Benazir returned to Pakistan earlier, it was widely believed that her return was sponsored by the United States. Her statements later confirmed that she would fully cooperate with the US in all matters including "war on terror", access to A.Q. Khan, allowing US troops to enter the Pakistani territory to fight the Taleban and Al-Qaida etc. These promises of collaboration with US went far beyond anything Musharraf was willing to do for the US. It was a no-brainer for Mehsud and his allies to see Benazir as a threat.