Evan (the abducted kid) takes off his right earphone twice as Chase (the killer) knocks on the car window. (Seen once from the outside camera and then from the inside camera.)
When Chase holds a knife to Evan's throat, it bounces into position, revealing that it's made of rubber.
In Chase's flashback to his father attempting to revive him, when young Chase is lying on the ground, you can see his chest rise.