I agree w/the comments of Burgess159, plus add the facts (as I understand them from news sources)  that the shooter had full body armor, including helmet, throat protector & groin protector, as well as a gas mask. I suppose some of the CC crack shots that exist could've aimed for the few soft spots around the armor & maybe slowed the guy up a little...again assuming you could see thru the people, darkness (darkened theatre) & gas, while of course not being killed by one of his hundreds of semi-automatic projectiles. I'm also not clear if other attendees in this theatre had "costumes" on or not. If so, I guess you just shoot for the guy w/the costume on.....

Re. whether the gunman would've proceeded w/his actions if he knew some movie-going citizen was waiting for him with a loaded pistol vs the criminal's AR15, shotgun, 2 pistols, and tear gas.....I suspect he would've proceeded anyway, as well as most other horrendous mass killers would've. I believe they welcome their termination in a blaze of glory, whether self-inflicted, or by another's weapon. I'm really surprised this guy surrendered. That is not the usual ending. They usually don't do this to create a better tomorrow for themselves or their families.

Re. killing him immediately or later....it would be beneficial to the world if they can get more info out of him first to help understand & therefore prevent future wack-os. I'd recommend some waterboarding to help him divulge the "why", then proceed with orderly punishment.

Finally, I read that some responders here say that irregardless of the signs or rules stating no CC in the Colorado theatre, they would've had theirs anyway. So....that makes me wonder, how many cc pistols were in the theatre since there are many others that probably  think like NAT-ers. Should we assume there were some? Or none?

Of courese Ariz had CC rights when Giffords was shot last year. There were CC-ers in the crowd then, but of course the heroes of the day were only using their wits & brawn. I have read accounts saying there were other CC-ers in the crowd of onlookers. Keep in mind, the CC-ers could've shot each other in such pandemonium. Just WHO is the criminal might've been hard to ascertain.

http://www.msnbc.msn.com/id/41018893/ns/slate_com/t/armed-giffords-hero-nearly-shot-wrong-man/

Loughner allegedly proceeded to fire apparently randomly at other members of the crowd.^[2][20] The weapon used was reported to be a 9mm Glock 19 semi-automatic pistol with a 33-round magazine.^[21][22] A nearby store employee said he heard "15 to 20 gunshots".^[23] After the gunman ran out of ammunition in the first magazine, he stopped to reload, but dropped the loaded magazine from his pocket to the sidewalk, from where bystander Patricia Maisch grabbed it.^[24] Another bystander clubbed the back of the assailant's head with a folding chair, injuring his elbow in the process, representing the 20th injury.^[25] The gunman was then tackled to the ground by 74-year-old retired US Army Colonel Bill Badger,^[26] who himself had been shot, and was further subdued by Maisch and bystanders Roger Sulzgeber and Joseph Zamudio