The shooting at the movie theater is a horrible and terrible event. Rightly causing outrage in any decent human being. So I don't begrudge that sentiment nor the call to action to avoid it in the future.
I suspect there will be the usual call for more gun control. The investigation will reveal, I'm sure, whether the suspect was legally allowed to own firearms. If he wasn't, then the problem isn't the laws.
If he was legally allowed to have them, then I wonder what "lunatic detector" anyone has in mind that could have been applied and was not.
We must be wary of trampling rights in response to tragedies.