Investigators looking for clues to the motive behind a shooting rampage at a screening of the new Batman movie sought to enter the suspect's elaborately booby-trapped apartment today.
As the suburb of Aurora in Denver, Colorado, grieved, police warned that removing trip wires could detonate the explosives.
The FBI and Homeland Security Department said there was no information to indicate that more shooting sprees were planned at cinemas around the US, according to an intelligence bulletin obtained by The Associated Press.
Twelve people were killed and 58 others injured in yesterday's attack. A few of those suffered injuries not from shots but in the chaos that ensued as the audience tried to flee the smoke-filled theatre in a panicked dash for the doors, authorities said. Among the wounded, 11 were said to be in a critical condition.
It remained unclear today what drove the suspect, identified as James Holmes, 24, to fire round
after round at the unsuspecting audience watching The Dark Knight Rises.
After the shooting, police said they found that Holmes's nearby apartment had been booby-trapped and ordered residents in the building and surrounding homes to evacuate.
Authorities were not able to enter the apartment last night. Scores of law enforcement officials, including local bomb squad technicians and dozens of federal Bureau of Alcohol, Tobacco, Firearms and Explosives agents gathered again at the apartment today.
"It's safe right now with the evacuations so we don't want to rush anything," said Aurora Police Sergeant Cassidee Carlson.
The apartment contains jars of unknown accelerants and trip wires, she said, noting that authorities may be forced to detonate the explosives.
Fire crews stood by ready to fight any ensuing blaze.
Police grimly went door to door late 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 dead 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 that he had bought 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 also was 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 new 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.
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 had spoken to Mr Kelly. The two used to work together in New York.
Asked whether Holmes had 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. Up the hill, about 20 pastors led a vigil for about 350 people, some hugging and crying. A sign read "7/20. Gone Not Forgotten".
An emotional Colorado Governor John Hickenlooper said earlier today 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 to The Dark Knight Rises, went into the cinema as part of the crowd and propped open an exit door as the film 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, Tanner 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 theatre.
Within minutes, frantic emergency calls brought some 200 police officers, ambulances and emergency crews. Holmes was captured in the car park.
Kaitlyn Fonzi, a graduate student at University Hospital who lives in the apartment below, said she heard loud music coming from the suspect's unit just after midnight.
She went upstairs and put her hand on the door handle. She felt it was unlocked, but she did not know if he was there and decided not to confront him.
Instead, she called police, who told her they were busy with a shooting and did not have time to respond to a noise disturbance. She said she was shaken to later learn the apartment was booby- trapped.
"I'm concerned if I had opened the door, I would have set it off," she said.
The shooting was the worst in the US since an attack in 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 which said: "Our hearts go out to those who were involved in this tragedy and to the families and friends of those involved."