As with John F. Kennedy, it’s unlikely that there is one single reason that Benazir Bhutto was killed. But here’s one you probably haven’t heard: The competition for pipeline rights in Pakistan’s next-door neighbor, Afghanistan.
Bhutto’s one mistake: she vehemently supported the pipeline proposed by Argentinian oil company Bridas, and opposed the pipeline by Unocal (favored by the US). This contributed to her ouster in 1996, and the return of Nawaz Sharif to power. As noted by Rashid:
“After the dismissal of the Bhutto government in 1996, the newly elected Prime Minister Nawaz Sharif, his oil minister Chaudry Nisar Ali Khan, the army and the ISI fully backed Unocal. Pakistan wanted more direct US support for the Taliban and urged Unocal to start construction quickly in order to legitimize the Taliban. Basically the USA and Unocal accepted the ISI’s analysis and aims—that a Taliban victory in Afghanistan would make Unocal’s job much easier and quicken US recognition.”
However, Bridas outmaneuvered Unocal by aligning with Prince Turki el-Faisal, the Saudi intelligence chief and mentor to Osama bin Laden. Osama advised the Taliban to sign with Bridas, and it appeared the Argentinian firm had trumped Unocal — until 9/11, after which all deals were off.
Update: After thinking about it a while, I have to discount this theory. If Benazir Bhutto was really such a threat to Western oilmen, she could have been taken out in 1996.