Jason Burke, blogging in the Guardian, speculates that it may be a combination of many factors:
“Finally, it is worth looking back at a previous attempt on Bhutto's life - not that of October 18 this year but back in the early 90s, when Ramzi Yousef, now in prison in America for trying to blow up the Twin Towers, attempted to assassinate her. That scheme involved local criminal elements, senior Islamic militants from the Gulf, a local Afghan hardline commander with Saudi Arabian links, Yousef himself and money from overseas. A similar combination may be behind this murder. It is unlikely, sadly, that we will ever really know.”
Bill Roggio, writing in the Weekly Standard, argues that the attack had the hallmarks of a military operation and was probably carried out by the Taliban and al-Qaeda. Bob Novak who has excellent sources in Washington, writing a column speculating upon this question a couple of months ago after the last major attack upon her, said:
“So, who wants to kill Benazir Bhutto? Not Musharraf, who is astute enough to know his complicity in her death would be devastating for him. Yet he has not been forthcoming in investigating the Oct. 18 bombing in Karachi or preventing its recurrence…
Al Qaeda and the Taliban, who do not want Bhutto to lead Pakistan's government a third time, are behind the suicide bombing but do not appear to have acted alone. In addition to the bombing that took at least 136 lives, it is unpublicized that snipers fired on her convoy. Not al Qaeda's style, that points to Pakistan's ISI (Inter-Services Intelligence), or at least rogue elements within it. Musharraf, though still military commander, does not exercise complete control over ISI (which is considered a state within a state and gave birth to the Taliban in Afghanistan).
It is difficult to identify attempted assassins because Interior Minister Aftab Khan Sherpao said he would "categorically reject" help from world-class FBI forensic investigators…More than 10 days after the bombing, it is too late for forensic evidence.”
Burke now, as Novak then, thinks that Musharraf is probably not involved. Given the history of political assassinations in Pakistan, as Burke concludes, sadly, the truth may never be known.