At the end of the film, David, now Adam, could not possibly expect his next ruse to work. After all, he left everyone else alive, sans Jay, Mrs. Cutter, and Susan's friend, being they were all about to talk to the police. Jay found out he never went to the University Of Oregon, Mrs. Cutter recognized him from "America's Most Wanted", and Susan's friend was trying to get Jay to do a background check on David. With the remaining family left alive, they could all call "America's Most Wanted" and say that the man living with them was the same man wanted for the previous killing. David, now Adam, does not don a very convincing disguise at the end being his face is the same, he has practically the same hair color, and is still clean shaven. The only difference is he now has longer sideburns. Isn't it possible someone else will recognize him wherever he is now?