Police are probing a shooting rampage in the US state of Colorado where a masked gunman killed 12 people and wounded 58 others during a showing of the new Batman film "The Dark Knight Rises".
Police arrested a man, James Holmes, shortly after the incident in a Denver suburb on Friday and are now considering sending a robot into his apartment to detonate what they say is a sophisticated booby-trap.
Holmes, 24, is accused of storming into a cinema in a shopping mall in Aurora clad head-to-toe in black body armour and a gas mask. He reportedly tossed smoke bombs into the audience before shooting seemingly at random.
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The graduate student, who authorities said had dyed his hair red and called himself "The Joker" in a reference to Batman's comic-book nemesis, was taken into custody in a car park outside the cinema. He was in possession of a rifle, handgun and a knife. Police said he did not put up a fight.
Police later found a set of explosives at his home following the arrest, but they have been unable to enter. "His apartment is booby-trapped, Aurora Police Chief Daniel Oates said.
"We are trying to determine how to disarm the flammable or explosive material. We could be here for hours or days.
"The pictures are fairly disturbing. It looks very sophisticated, how it's booby-trapped. It could be a very long wait," he said.
Oates said authorities had determined the apartment was too dangerous for officers to enter and would send a robot in to detonate the explosives after consulting with federal authorities.
Meanwhile, hours after the shooting, a makeshift memorial with 12 candles in a row and piles of flowers sat at a corner near the entrance to the movie theatre parking lot. Up the hill from there, about 20 pastors led an emotional vigil for about 350 people, some hugging and crying.
Chris Henderson, Aurora's deputy fire chief, said Holmes' living room was found crisscrossed with trip wires connected to
what appeared to be plastic bottles containing an unknown liquid.
James Holmes, 24, was a PhD student of neuroscience at the University of Colorado
He lived in an apartment in the north of Aurora, only eight kilometres from the cinema
He has no previous criminal record and is in police custody
A law enforcement source told the Reuters news agency the suspect had also set a timer to turn on loud music in his apartment - playing the same song over and over again - apparently in an attempt to prompt a complaint and lure police into a trap.
"If he was shot and killed, it is without a doubt that these ... booby traps were there to murder and inflict casualties upon first responders," the source said.
With Holmes in jail and awaiting an initial court appearance on Monday morning, police have declined to reveal what he has told investigators and would not discuss possible motives for the shooting rampage.
Meanwhile little has surfaced from the suspect's past to suggest he was capable of such violence.
Raised in a middle-class San Diego neighbourhood, he earned a degree in neuroscience from the University of California at Riverside before seeking his graduate degree from the University of Colorado.
Holmes was described by acquaintances as bright but was in the process of dropping out of his graduate programme at the time of the shooting, according to the university.
The shooting stunned Aurora and much of the nation, evoking memories of the 1999 massacre at Columbine High School in Littleton, 27km from Aurora, where two students opened fire and killed 12 students and a teacher.
It also resonated in the US presidential race as both President Barack Obama and his Republican rival, Mitt Romney, toned down their campaigns, pulled out their advertisements from Colorado and dedicated their scheduled events to the victims on Friday.
Witnesses at the movie theatre told of a horrific scene, with dazed victims bleeding from bullet wounds, spitting up blood and crying for help. Among those taken to hospitals as a precaution was a baby boy.
Confusion reigned as shooting broke out during an action scene in the summer blockbuster. The suspect may have blended in with other movie-goers who wore costumes as heroes and villains, and some witnesses said they believed at first that his appearance was a theatrical enhancement to the film.
The gunman "appeared at the front of the screen" in the theatre and started shooting, Police spokesman Frank Fania said on Friday.
He said police received the first call about the shooting at 00:39 local time and responded within "a minute or two". Local hospitals were alerted to a "mass casualty incident".
"This is a horrific event," police chief Oates said on Friday
He said 10 people were killed on site and the other two were later reported dead in area hospitals.
The gunman was armed with an AR-15 assault rifle, a 12-gauge shotgun and a Glock .40 calibre handgun, Oates said.
Police found an additional Glock .40 calibre handgun in his car, parked just outside the theater's rear emergency exit, Oates said.
He was dressed entirely in black with a gas mask, ballistic helmet, tactical ballistic vest, throat guard, leggings and crotch guard, Oates said, adding that Holmes had purchased the weapons legally at three local gun stores in the last 60 days and had bought 6,000 rounds of ammunition.