If he'd been truly paying attention, Batman would have seen Jason shifting in the seat, subtle as it had been. He would have known that something was definitely amiss and to back off because Jason was pretending. But Bruce hadn't seen it. The love, yes love, he had for his disillusioned ward overrode his common sense.
Not feeling any life threatening injuries, Batman gently as possibly extracted Jason from the car. He was heavy, but Batman didn't let the strain of carrying Jason show. He walked over to the Batmobile and carefully set the former Robin down on the ground before turning back to the car. He reached into one of his many utility pouches on his belt and pulled out a small pressurized tube. Hitting the nozzle, he sprayed it all over the cop car to wash away any and all of Jason's prints.
Satisfied, he replaced the cannister and stepped back from the car. It was time to get Jason to a safe house, treat him, then try to make him see reason.