(at around 28 mins) As David and Colby are staking out the house and the teenager comes out and walks to his car the trunk is clearly open, yet a few seconds later when he reaches it we see it is closed tight.
When Gregory runs from the car the camera angle changes and the car has disappeared completely.
During the interrogation Megan refers to the Gun as "A Semi-Automatic weapon". A Mac-10 as is shown is fully-automatic. Semi-automatic weapons only fire 1 round per trigger pull, Full-auto keeps firing while you hold the trigger down.