(AP) - Police say at least 12 people are dead and 50 injured following a shooting at a movie theater in Aurora, Colo.

Police say the gunman opened fire shortly after midnight local time in a theater during a showing of the latest Batman movie "The Dark Knight Rises."

Witnesses tell police that before the gunman started shooting, he released some sort of canister, and then there was a hissing sound and some gas emerged.

Officials say police ambulances and emergency crews swarmed on the scene after frantic calls started flooding the 911 switchboard.

Police found the gunman near a car behind the theater and took him into custody. Aurora Police Chief Dan Oates says a "gas mask, rifle, handgun and at least one additional weapon" were found inside the theater.

Oats says the man taken into custody also mentioned "possible explosives in his residence," so officials are also dealing with that potential threat.