By NBC News' Pete Williams and NBC News staff
Updated at 11:11 a.m. ET: Twelve people were killed and at least 50 others wounded early Friday when a gunman wearing a bulletproof vest opened fire during a midnight premier screening of the latest Batman movie near Denver, authorities and witnesses said.
The apartment of the suspect in custody, named as 24-year-old James Holmes, had been booby-trapped with what police described as sophisticated explosives or flammable material and officers were trying to determine how to defuse the device or devices, Aurora Police Chief Dan Oates said. The area had been evacuated, and police were expected to remain on the scene "for hours or days," he said.
The victims of the cinema shooting were being treated in at least six hospitals included a 6-year-old. The youngest person treated was a 4-month-old baby, who has been released. The oldest reported patient is 45.
Authorities said the gunman had appeared at the front of the theater during the film and released a canister of tear gas. Witnesses told reporters that the gunfire erupted during a shootout scene in "The Dark Knight Rises."
"It was mass chaos," witness Jennifer Seeger told TODAY. The gunman shot the ceiling and then "he threw in the gas can, and then I knew it was real."
"I told my friend, 'We've got to get out of here,' but then he shot people trying to go out the exits," she recalled. She said the shooter made his way up the aisle, shooting as he went, saying nothing.
Oates initially told journalists that 14 people had been killed but the figure was later lowered to 12.
The shooting occurred in the Century 16 Movie Theaters at the Aurora Town Center. Aurora is a suburb less than 10 miles east of downtown Denver.
NBC station KUSA-Denver cited a witness as seeing a black-clad 6-foot-tall man wearing a riot helmet, goggles and bullet-proof vest. However, many people attended the film dressed in Batman-related costumes. Witnesses said the gunman entered the theater through an emergency exit door. The suspect was found in possession of a gas mask, Oates said. Ammunition was found in the suspect's car, police said. The shooter had three weapons -- an assault-type rifle and two handguns, officials told NBC News. Holmes' car has Tennessee plates but authorities said he lived locally. Police said there was no evidence of additional suspects. "We're pretty confident he acted alone," officer Frank Fania told TODAY.
An FBI official told NBC News that the agency was working with local authorities on the investigation, but that there was no early indication of a link to terrorism. Holmes was not on any federal law-enforcement watch lists, authorities told NBC News. President Barack Obama cut short a campaign visit to Florida to return to Washington ahead of schedule.
He called for reflection after the attack. "There are going to be other days for politics," Obama said during an abbreviated appearance in Fort Myers, where he led a moment of silence on behalf of the victims and their families.
'Get us some damn gas masks'
Police raiding the theater in the hunt for the suspect had to ask for gas masks.
"Get us some damn gas masks for theater 9, we can't get in it," one officer radioed back to emergency dispatch during the operation, according to an excerpt aired on KUSA.
Moviegoers described scenes of chaos and terror inside the movie theater. Seeger told TODAY there were "a lot of children" in the theater. "When I ... tried to escape, there was a little girl, 12 or 13, just laying lifeless on the stairs," she said. "I got terrified. I didn't know what to do, like a deer in the headlights. I jumped into the aisle and curled up into a little ball waiting for him to go away," she told TODAY. "I have never been more scared then the moments where we were all trapped in the theater, helpless. Unable to get out at all," another moviegoer, Rachel Fedeli, posted on Twitter.
Tanner Coon, who was in the theater with a friend and the friend's 12-year-old brother when the shooter came in, said he told them to "get down" when he heard the gunshots. The shooter fired off about 20 rounds and there was then a pause and a "period of quietness when everybody started running out," Coon said. " I slipped on some blood and landed on a lady. I shook her and said we need to go. There was no response so I presume she was dead," Coon said.