So the fake fireman/prisoner helps them and is super nice with them the whole movie and then one of the girls find out he's a prisoner, so he suddenly turns evil and wants to kill them? What the hell? The movie was actually pretty good before that.
CG GORE IS THE WORST THING THAT HAS EVER HAPPENED TO THE HORROR GENRE!
I would agree. What difference did it make if any of the girls knew he was an escaped convict? Even then, if he was always a convict, why remove the fireman's jacket and expose himself like that?
They could have easily just had the fireman hold the sister hostage, they agree to go their separate ways if they make it, aftershock knocks rocks on fireman/crook and younger sister, older sister either has moment to say goodbye or younger sister is instantly dead, cut to the end that we see.