it's completely unrealistic that Jerry would never find out about what happened to Gary

After Gary didn't show up to meet with Chrissy, Jerry would have tried to find out what happened to him. It would be very easy for him to find people who would know what happened to Gary. Jerry had been to both Gary's mom's house and Gary's church. He could have just gone over to talk to Gary's mom or the members of his church to ask about what happened to him and they would tell him about the car crash. If the movie were realistic Jerry would have done at least one of those things at the very latest by the next day. Once he knew that Gary didn't show up to meet with Chrissy because he died in a car crash he would know that Gary was the killer and feel vindicated.