....only one of them survived so who exactly told the story of events if the survivor, the guy was locked up while the girls were killed? No bodies were found either. It's possible that small pieces of the story could have come from the video footage, but they didn't film the whole thing. The guy, Ben Mitchell (who the character was based on) was cleared of all suspicion after four months in custody.
It's also been suggested by some, that although the guy tried to escape last, that he actually was the first, and that the rest of the movie with the girls, happened later but was shown first, if you see what I mean. They come to this conclusion by looking at the condition of the surroundings, the yard and the state of the vehicles.
I don't subscribe to this theory because I simply can't be bothered to dissect it forensically, but if it's correct, it means he would have left them there to be tortured and die.