If all it took were a new law, then the old one banning mass murder would have stopped this shooting.
It's kind of hard to argue against anti-gun proponents... since the shooter bought everything legally. Most of the cases of mass killing sprees we've had, the shooters have bought the guns legally and planned it for months. You would make more sense if there was a strong correlation between these killing sprees and unlawfully attained weapons.
Yes, since a person deranged enough to go on a mass shooting spree wouldn't have to motivation to find alternatives means....... Would it have been better if they were killed with an illegal weapon? Would it make it more acceptable in your eyes? Or maybe it would have been better if he would have just set off a bomb in the theater? As long as you feel better...right?