There are many questions in minds of about the killing of Benzir Bhutto. Who killed her, Pakistan military agencies? or Taliban/Alqaida? or America or any other? I think the answer lies who will get the most benefit.
Let's take the first suspect, Mushraf will get the following benefits, extend his rule to country and make more money from inside as well as from foreign on the name of "war on terror". The military will use some of this money to strength itself while rest will go in same pockets where it used to went. The other reason which let us to think is an email and Text messages from Benzir, in which he directly blame Musharf and military.
The second suspect are Taliban/Alqaida, the benifit they can get is an image of a powerful authority who can do any thing in the country, which can result some settlement with government in Tribal, Swat areas. On other hand they will loss their support not only from rest of Pakistan but also from Tribal areas I don't think they are so idiot to divert the people's anger to ward them.
The third suspect is America. America has eye on the nuclear weapons of Pakistan so he will like to have the control if the country goes toward civil war, as current situation seems. For this he already had done exercise.
The exact answer will never be revealed, we have to make guesses. what ever it is, it was a planned and might be above mentioned forces made it combine?