[Personal Speculation] The Bin Laden posed a threat to the Saudi's. They had evidence of direct Saudi involvement in 9/11. ( conspiracy )

submitted by Hyper_threaded

The Saudi's really want out of this 9/11 lawsuit. I think that the BL's unsuspectingly trusted a flight to break bread with the royal family. The family decided that it was easier to tie up loose ends as apposed to negotiate a verbal agreement that might not have lasted. Thus the Saudi Royal Family did the necessary.

Tl;DR the Bin Ladens were killed to silence their proof of SRF involvement in 9/11 so as to not threaten Saudi removal from 9/11 lawsuit