Police have began disarming trip wires and explosive devices "set up to kill" inside the apartment of the suspect in the deadly Colorado movie theater shooting, hoping to find clues to his motive without destroying key evidence in a blast.
Authorities on Saturday detonated one small explosive and disarmed another inside James Holmes' suburban Denver apartment with a "water shot" device that emits a shock wave and water, a law enforcement official said.
Holmes is suspected to be the masked gunman who killed 12 people and wounded 58 others during a showing of the new Batman film "The Dark Knight Rises".
His apartment appears to have three types of explosives - jars filled with explosives, chemicals that would explode when mixed together and more than 30 "improvised grenades".
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Makeshift memorials sprang up for the victims, including a six-year-old girl, an aspiring female sportscaster and a man celebrating his 27th birthday, after police grimly went door to door with a list of those killed in the worst mass shooting in recent US history.
Holmes, 24, was arrested early on Friday outside the Aurora theatre after witnesses say he unleashed gunfire and gas canisters on a crowd of people.
The devices in Holmes' booby-trapped apartment were "set up to kill that person and that could have been a police officer executing a search warrant," Aurora police Sergeant Cassidee Carlson said.
Police planned an intricate procedure to disarm the possible weapons without destroying evidence that could be in the apartment.
"We don't want to lose evidential value," Carlson said.
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
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.
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
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.