AURORA, Colo. (Reuters) - A gunman in a gas mask and bullet-proof vest killed 12 people at a midnight premiere of the new "Batman" movie in a suburb of Denver early on Friday, sparking pandemonium when he hurled a gas canister into the auditorium and opened fire on moviegoers.

The attack injured 59 others including children during a screening of "The Dark Knight Rises" at a mall in the suburb of Aurora, which turned into a chaotic scene of bleeding victims, horrified screams and pleas of "I'm hit, help me," witnesses said.

The suspect also booby-trapped his Aurora apartment with sophisticated explosives, creating a hazard for law-enforcement and bomb squad officers who swarmed to the scene. Authorities evacuated five nearby buildings, and created a perimeter of several blocks.

Officers took the suspect into custody in the parking lot behind the cinema, where he surrendered without a fight, police said.

He was armed with a high-powered rifle, a shotgun and two pistols, according to a law enforcement source close to the investigation.

The suspect was identified as James Eagan Holmes, 24, 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. His family issued a statement of sympathy for the victims and asked for privacy while they "process this information."

The living room of the suspect's apartment was crisscrossed with trip wires connected to what appeared to be plastic bottles containing an unknown liquid, said Chris Henderson, Aurora's deputy fire chief. Authorities planned to detonate the suspected explosives with a robot, he said.

"The pictures are fairly disturbing. It looks very sophisticated, how it's booby-trapped. It could be a very long wait," Aurora Police Chief Dan Oates told reporters.

The gunman appeared at the front of the theater during the movie and released a canister which let out a hissing sound before gunfire erupted, police said.

"When we got out of the theater it was just chaos. There was this one ... guy, was on all fours crawling. There was this girl spitting up blood," witness Donovan Tate told KCNC television. "There were bullet holes in some people's backs, some people's arms. There was this one guy who was stripped down to just his boxers. It looked like he was shot in the back or something. It was crazy."

Confusion reigned as shooting broke out during an action scene in the summer blockbuster, one of the more highly anticipated films of the year. 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," witness Jennifer Seeger told NBC's "Today."

Chandler Brannon, 25, who had been watching the movie with his girlfriend, said that about 20 minutes into the movie he saw a smoke bomb go off and heard what sounded like fireworks. He later realized they were a rapid volley of gunshots.

"I told my girlfriend to just play dead," he told Reuters. "All I could see was a silhouette."

CAMPAIGN TAKES A DAY OFF

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 November 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, Florida, which he cut short to address the shooting.

White House officials saw no connection to terrorism, an Obama spokesman said.

Obama's opponent, Republican presidential candidate Mitt Romney, pulled all television ads in Colorado until further notice, campaign spokeswoman Andrea Saul said, and a scheduled campaign was dedicated to addressing the shooting.

MEMORIES OF COLUMBINE

The shooting evoked memories of the 1999 massacre at Columbine High School in Littleton, also a Denver suburb and 17 miles from Aurora, where two students opened fire and killed 12 students and a teacher.

Six Aurora-area hospitals reported receiving 55 patients from the scene. Ten victims died in the theater and two died in the hospital, Aurora Police spokesman Frank Fania told NBC.

"This is one of the most horrific nights I've ever had to work," said Comilla Sasson, an emergency doctor at University of Colorado Hospital in Aurora where 22 patients ranging in age from three months to 45 years arrived in private cars, police cars and ambulances.

U.S. military personnel apparently were among the casualties but it was not immediately clear whether any were killed, the Defense Department said.

Buckley Air Force Base is the largest employer in Aurora, a city of more than 320,000 people, according to the Aurora Economic Development Council.

"Our hearts go out to those who were involved in this tragedy and to the families and friends of those involved," read a statement from Holmes' family in San Diego that was read by police there.

The family, which said it was cooperating with authorities, asked for privacy.

SECURITY PRECAUTIONS

In New York, police will deploy officers at screenings of "The Dark Knight Rises" throughout the city "as a precaution against copycats," Police Commissioner Raymond Kelly said in a statement.

The Paris movie premiere was cancelled on Friday, event organizers said. Workmen cleared away barriers that had been set up in preparation for the premiere at a cinema on the capital's Champs Elysees avenue.

"Warner Bros. is deeply saddened to learn about this shocking incident. We extend our sincere sympathies to the families and loved ones of the victims at this tragic time," said Jessica Zacholl, a spokeswoman for Time Warner-owned Warner Bros., the studio behind the film.

The film, with a budget of $250 million, opened on 4,404 screens, the second widest release ever behind "Twilight: Eclipse," and industry analysts had said it stood a good chance of matching or beating the opening weekend box office record of $207 million set by Disney's "Avengers" in May.

The prior release in the Batman series, "The Dark Knight," has grossed more than $1 billion at the worldwide box office since its release in 2008.