One thing I read earlier in another thread here, and I think it may shed some light on people's hesitancy to point fingers just yet: suppose if, just if it wasn't bin Laden. (Suspend your disbelief for the moment.) If he really didn't cause it, and yet we spend all our energy going after him, then whoever really did do it will still be out there and able to strike again. From a practical perspective, they need to make sure they don't miss somebody, so they have to be very thorough.