AURORA, CO -- A gunman in a gas mask and body armour killed 12 people at a midnight premiere of the new Batman movie in a suburb of Denver early Friday, opening fire on moviegoers after hurling a gas canister into the theatre.

Armed with an assault rifle, a shotgun and a pistol, he wounded another 58 with gunfire during a screening of The Dark Knight Rises at a mall cinema, which turned into a chaotic scene of bleeding victims, horrified screams and pleas for help, witnesses said.

A suspect, 24-year-old James Holmes, was arrested immediately afterward in the parking lot and reportedly did not resist arrest.

Local police, who are heading up the investigation with help from the FBI, said his nearby apartment was booby-trapped with "very sophisticated" explosives and buckets of ammunition. They evacuated the building and nearby homes as a precaution.

Jennifer Seeger was sitting in the second row of Theatre 9 at the Century 16 cinemas when the lone gunman entered the theatre through the emergency exit, set off a container of tear gas and began shooting.

"I was the very first person he saw," the 22-year-old Aurora resident told QMI Agency. "I was standing four feet away from this guy, and he took his gun and pointed it right in my face."

"I dove into the aisle and tucked myself under the chairs as far as I could with other people. We were just pushing our bodies together, trying to stay still."

As the much-anticipated premiere of The Dark Knight Rises played on, the crowd was thrown into "mass chaos," blinded by tear gas while rushing for the exit in the still-darkened cinema.

"He was looking for immediate gratification and was shooting at all those people who were trying to flee," Seeger said. "It was like if he didn't see you, he didn't shoot you."

Moviegoer Eric Hunger, who was watching the Batman movie in Theatre 8 just next door, at first thought the shots were part of the experience.

"We thought the theatre was trying to do something with effects -- you know, to make it more enjoyable," he told QMI Agency. "But as more and more smoke came in (to Theatre 8), we started to get more worried. When more shots starting hitting the wall, that's when people started to get up and try to get out."

The gunman may have blended in with other moviegoers who wore costumes as heroes and villains.

"He looked like he was in the military or like he was a SWAT person, so he just kind of blended in with the chaos of the crowd. People thought he was probably like a cop or something," Seeger told NBC's Today.

Holmes is a University of Colorado medical school student who was in the process of dropping out of a graduate program in neurosciences, the university said in a statement.

Holmes had only a speeding ticket on his criminal record and was dressed in black with a gas mask, ballistic helmet, vest, throat guard and crotch guard, police said.

His family issued a statement of sympathy for the victims, saying "our heart goes out" to their loved ones, while they also asked for privacy from the media while they "process this information."

The youngest reported fatality is a six-year-old girl, and a three-month-old baby was reportedly wounded in the massacre.

Police have cordoned off the entire parking lot of the Century 16 theatre complex, which is attached to a large suburban shopping mall.

Local streets, too, have been cordoned off as police continue to comb through the crime scene for evidence.
U.S. President Barack Obama, who was notified of the shooting early on Friday morning by his homeland security adviser, John Brennan, urged Americans to "stand together" with the people of Aurora and said political campaigning ahead of the Nov. 6 election should be set aside.

"There are going to be other days for politics. This, I think, is a day for prayer and reflection," Obama told supporters at a previously scheduled campaign event in Fort Myers, FL, that he cut short to address the shooting.
The Denver suburbs are no stranger to tragedy.

In 1999, 12 students and a teacher were shot and killed at Columbine High School in Littleton, Co., which is about 30 kilometres from Aurora.

Twenty-six others were wounded in that five-hour shooting rampage, after which the two gunmen -- students themselves -- killed themselves in the school's library.

-- with files from Reuters