The briefcase bomb
How could Aaron's character be sure the bad guy wouldn't open the briefcase enough to detonate the bomb when he was standing next to him? If I was the Hallgate guy, I would immediately make sure that the documents were indeed the ones in question - not fake ones. Even if he knew the case would not be opened immediately, how could he be sure he would be placed in the different car as the target?
The only explanation I can think of is that he just took that risk and his main goal was to kill the bad guy to eventually protect his daughter from him even if it meant dying for her. But then again wasn't she at first in proximity of the briefcase also?