Police in the US state of Colorado have entered the booby-trapped apartment of a masked gunman who killed 12 people and wounded 58 others during a showing of the new Batman film "The Dark Knight Rises".
Authorities said on Saturday that they were using a robot to make their way into the heavily booby-trapped home of James Holmes, a 24-year-old student arrested shortly after allegedly committing the murders in a Denver suburb a day earlier.
Sergeant Cassidee Carlson, a local police spokeswoman, said officials had disarmed the trip wire and the first explosive device in the apartment, which was set up to kill the person opening the door.
"This is some serious stuff that our team is dealing with," Carlson said.
She said that there were other devices that need to be disarmed but authorities are reassessing the scene.
Tripwires, ammunition and jars of explosives are scattered in the shooter's Aurora apartment, officials said, positioning vehicles and personnel around the apartment building.
Holmes 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.
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.
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.
Motives for shooting
Chris Henderson, Aurora's deputy fire chief, said Holmes' living room was found criss-crossed 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.