http://www.youtube.com/watch?v=S3K783ivyY8&feature=related

Benazir Bhutto believed Usama bin Laden was already dead, and had been "for years" in this 2007 interview, done shortly before she herself was assassinated.  Certainly, she may have been misinformed... and I doubt her mentioning UBL was the reason she was killed; the assassins had been trying to get her for some time.

Maybe we did kill him in Tora Bora when those caves were blown apart... 

Then who did SEAL Team 6 kill?