Revealing mistake: When the killer is up in the radio tower, he tries to force the man up the ladder. He brandished a revolver and you can hear the hammer being cocked back. It shows the revolver more and you can see the hammer is still down.
Audio problem: In the beginning of the movie when Billy is looking for Penny, he is going all over the place trying to find her and when Penny is looking for Walt Jr., she is going all over the place trying to find him. Why don't they just use the speaker Penny uses to call for Billy and to tell her co-workers that the police have located the killer?