US police have begun the intricate process of disarming booby traps in the apartment of the suspect behind the Colorado cinema shootings, hoping to find clues to the motive for the rampage without causing an explosion that could destroy key evidence.
Scores of law enforcement officials, including bomb squad technicians and dozens of federal agents, removed one trip wire and one explosive device inside James Holmes's apartment today, and "other devices" are in there, Sergeant Cassidee Carlson said.
"We have been successful in defeating the first threat," she said, adding that the traps were meant to kill the first people entering the apartment in the Denver suburb of Aurora.
Holmes, 24, was arrested yesterday outside the suburban cinema with high-powered weapons and ammunition and charged with the rampage which killed 12 people and injured another 58 during the midnight showing of the new Batman movie, The Dark Knight Rises.
Makeshift memorials have sprung up to the victims, who included a US navy sailor, an aspiring sportscaster and a man celebrating his 27th birthday.
In his Saturday radio address, President Barack Obama urged Americans to pray "for the victims of this terrible tragedy, for the people who knew them and loved them, for those who are still struggling to recover".
Seven of the wounded remained in a critical condition in hospital today, some with injuries that could be permanent, a trauma surgeon said.
Police had delayed entering Holmes's apartment yesterday after learning it had been booby-trapped with trip wires and possible explosives, and evacuated several buildings around it.
Experts entered the apartment today and began to disarm the trip wires one by one to render them harmless, hoping not to detonate anything that could eliminate evidence against the suspect or information about a motive.
"We don't want to lose evidential value," Ms Carlson said.
About 30 ammunition shells and up to 30 other devices in the apartment also need to be disarmed, she said.
"A controlled detonation or another triggering mechanism" might be required, she added.
Police grimly went door to door yesterday with a list of victims killed in the worst mass shooting in the US in recent years, notifying families who had held out hope that their loved ones had been spared.
The victims included 23-year-old Micayla Medek, said Anita Busch, the cousin of Ms Medek's father. The family took the news hard, but knowing her fate after waiting without word brought them some peace, Ms Busch said.
"I hope this evil act, that this evil man doesn't shake people's faith in God," she added.
Besides Ms Medek, relatives confirmed that Alex Sullivan and Jessica Ghawi were among those killed, Mr Sullivan on his 27th birthday.
Aurora Police Chief Dan Oates said Holmes used a military-style semi-automatic rifle, a shotgun and a pistol to open fire on the unsuspecting film-goers. He had bought the weapons at local gun shops within the last two months. He also recently purchased 6,000 rounds of ammunition over the internet, the chief said.
The suspect's stellar academic record, apparent shy demeanour and lack of a criminal background made the attack even more difficult to fathom.
It was also not known why he chose a cinema to stage the assault, or whether he intended some twisted, symbolic link to the film's violent scenes.
The Batman movie, the last in the trilogy starring Christian Bale, opened worldwide yesterday with midnight showings in the US.
The plot has the villain, Bane, facing Bale's Caped Crusader with a nuclear weapon that could destroy all of fictional Gotham City.
In New York City, Police Commissioner Raymond Kelly said: "It clearly looks like a deranged individual. He has his hair painted red. He said he was the Joker, obviously the enemy of Batman."
Mr Oates would not confirm that information, but did say he spoke to Mr Kelly. Asked whether Holmes wore make-up to look like the Joker, Mr Oates said: "That to my knowledge is not true."
Near the entrance to the cinema's car park, a makeshift memorial of 12 candles sat in a row alongside piles of flowers, and dozens of other memorials cropped up around Denver. Up the hill from the cinema, about 20 pastors led a vigil for 350 people, some hugging and crying. A sign read "7/20. Gone Not Forgotten".
An emotional Colorado Governor John Hickenlooper said earlier yesterday that people would not be defined by the tragedy.
"We are clear that we are going to rise back and lift ourselves above this," he said.
A federal law enforcement official said Holmes bought a ticket for the film, went into the cinema as part of the crowd and propped open an exit door as the movie was playing.
He then donned protective ballistic gear and opened fire, the official said.
Authorities said Holmes shot scores of people, picking off victims who tried to flee. At least one person was struck in an adjacent cinema by gunfire that went through the wall. Adding to the terror and chaos were two gas canisters thrown by the suspect that filled the theatre with smoke.
Tanner Coon, a 17-year-old Aurora resident who was watching the film with two friends, said he first thought the gunshots were firecrackers. When he realised what was happening, he ducked between seats and waited for the gunman to bark demands.
"When is he going to start telling us what to do? When is this going to become a hostage situation?" he said.
When the firing ended, the teenager said he started running up the row but slipped in blood and fell on a woman who was lying on the ground. He tried shaking her, he said, but she did not respond, so he left her behind and ran from the cinema.
The shooting was the worst in the US since an attack at Fort Hood, Texas, on November 5 2009. An Army psychiatrist was charged with killing 13 soldiers and civilians and wounding more than two dozen others. It was the deadliest in Colorado since the 1999 attack at Columbine High School, where two students killed 12 classmates and a teacher and wounded 26 others before killing themselves.
Holmes had enrolled last year in a neuroscience PhD programme at the University of Colorado-Denver, though he left last month for unknown reasons. In academic achievement, "he was at the top of the top", recalled Timothy P White, Chancellor at the University of California, Riverside, where Holmes earned his undergraduate degree before attending the Denver school.
Those who knew Holmes described him as a shy, intelligent person raised in California by parents who were active in their well-to-do suburban San Diego neighbourhood. Holmes played soccer at Westview High School and ran cross-country before going to college.
Police released a statement from his family yesterday that said: "Our hearts go out to those who were involved in this tragedy and to the families and friends of those involved."