KillerKiller (2007)

In the middle of nowhere, there lies a secure facility housing only serial killers. One morning the doors are open and the guards have vanished, but a strange freezing mist surrounds the building, preventing the inmates from leaving. Then, one by one, they are murdered. The survivors bicker, fight and blame each other, but the thing that's killing them looks suspiciously like a traditional 'victim'... A babysitter in a shower, a cheerleader, a camper...