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AURORA, Colo. (AP) - A gunman opened fire early Friday at a movie theater in a Denver suburb, killing 12 people and leaving at least 50 other injured.

The shooting occurred during a showing of the latest Batman movie "The Dark Knight Rises," police said.

Federal law enforcement officials say the suspect in Friday's deadly shooting in Colorado is James Holmes, a 24-year-old American.

The violence erupted about 12:30 a.m. MDT as the gunman stood at the front of one of the Century 16 theaters at the Aurora Mall.

"Witnesses tell us he released some sort of canister. They heard a hissing sound and some gas emerged and the gunman opened fire," Auror PD Chief Dan Oates said at a news conference.

There's no evidence of any additional shooters, Oates said.

ABC NEWS reports the gunman was captured with a rifle, handgun and a gas mask. There was no immediate word of any motive.

Witness Hayden Miller told KUSA-TV that he was inside Theater 16 and heard several shots.

"Like little explosions going on and shortly after that we heard people screaming," he told the station.

Hayden said at first he thought it was part of a louder movie next door. But then he saw "people hunched over leaving theater."

At least 48 people are being treated at Denver area hospitals after a mass shooting a movie theater - the youngest a 3-month-old baby.

Twelve people were taken to the Medical Center of Aurora with gunshot wounds that ranged from minor to critical. Three were treated for chemical exposure. They ranged in age from 16 to 31.

Denver Health had seven victims - one in critical and the rest in fair condition.

The University of Colorado hospital was treating 21 people, including the baby, all for gunshot wounds. The oldest patient is 45.

A 6-year-old was being treated at Children's Hospital Colorado, where a total of six victims ranging were taken. The oldest patient there is 31. Their condition wasn't known.

Aurora is located on the southeast outskirts of Denver, about 10 miles from downtown.

ABC NEWS reports no apparent ties to terrorism. 100 FBI agents are working with Aurora police.

Stay with KRGV and ABC News for continuing coverage.

(Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)