Yeah I realise that it's too hard to go back now. Honestly though even if the patrons had guns they'd be next to useless as he fired tear gas into the cinema first. If you were in there and had a gun, how do you shoot when you can't see? Or are you blasting away at random causing as much death and panic as the psycho?

However, if he couldn't get guns in the first place then the whole event likely either wouldn't have happened or at least not to the same degree.