Well, assuming the theoretical assassins had physical access to his car and world-class embedded systems expertise at their disposal, it would just be a matter

Well, assuming the theoretical assassins had physical access to his car and world-class embedded systems expertise at their disposal, it would just be a matter of locking his doors, disabling steering, disabling braking, and flooring the car's engine output. Unless the car is in the middle of nowhere, it's bound to hit something sufficiently lethal in a very short amount of time. That said, although peculiar given his line of work, I think it is premature for conspiracy theories at this point considering the near complete lack of information on the accident itself currently.