Or, - - -
One could say it's always a conspiracy.
al-Qaeda may well have done it. AND, someone could have relaxed the security enough to allow it to be done.
It wouldn't have to be done in unison or be jointly planned.
Bhutto was perceived, correctly, as America's shill, and 67% of Pakistanis regard the US as the greatest threat to their security. The security could have been patchy, knowing SOMEONE would get her. I think politics are so complex there that to expect a single cause is foolish. Too many had too much to gain and lose.
Arf