A gunman wearing a gas mask has killed 12 people when he opened fire at a Colorado cinema on the opening night of the latest Batman movie.
At least 50 others were injured. Police intially said 14 had been killed.
Federal law enforcement officials confirmed the suspect was James Holmes, 24.
Some movie-goers said they thought the attack was part of the show. Then they saw a silhouette of a person in the smoke at the front of the theatre, pointing a gun at the crowd.
“I told my friend, ’We’ve got to get out of here,’ but then he shot people trying to go out the exits,” Jennifer Seeger told NBC. She said the shooter made his way up the aisle, shooting as he went, saying nothing.
Some of the injured were children, with the youngest a three-month-old baby. Victims were being treated for chemical exposure apparently related to canisters thrown by the gunman. The gunman was arrested shortly after the midnight attack near a car outside the multiplex theatre in Aurora.
FBI spokesman Jason Pack said there was no indication in the investigation so far of any connection to terror groups.
President Barack Obama said he was saddened by the “horrific and tragic shooting.”
Aurora Police Chief Dan Oates said there was no evidence of other attackers. There was no immediate word of a motive.
“A gas mask, rifle, handgun at least one additional weapon (were) found,” Mr Oates said.
It was the worst mass shooting in Colorado since the Columbine High School massacre in 1999, where two students opened fire and killed 12 classmates and a teacher.
The suspect spoke of “possible explosives in his residence,” Mr Oates said. Police were at the Denver-area apartment and had evacuated the building’s other residents. He did not say whether explosives had been found.
He said police also checked for explosives at the theatre and secured those areas.
Movie-goers spoke of their terror as violence erupted.
Police officers ran in and told people to leave the theatre, Salina Jordan told the Denver Post newspaper. She said some police were carrying and dragging bodies.
Benjamin Fernandez, 30, told the Post he heard a series of explosions. He said people ran from the theatre and there were gunshots as police shouted “Get down!”
Mr Jordan told the paper one girl was struck in the cheek and others in the stomach, including a girl who looked to be around nine.
He said it sounded like firecrackers until someone ran into his neighbouring theatre yelling, “They’re shooting out here!”
KUSA-TV reported that some victims were being treated in hospital for chemical exposure, related apparently to canisters thrown by gunman.
Aurora is home to a large Defence Department satellite intelligence operation at Buckley Air Force Base.
[comment]See how the story unfolded this morning in our multimedia article[/comment]