Firefighters exit the apartment of the James Holmes
US police said Saturday they had defused the "major remaining threats" in the booby-trapped apartment of the gunman accused of the Batman theater massacre, which killed 12 in Colorado.
The progress was reported as the names of those who died early Friday were released -- including a six-year-old girl whose mother was also injured and two US servicemen.
The movie's star Christian Bale meanwhile voiced his sorrow at the shooting, and the studio behind "The Dark Knight Rises" said it was withholding box office data out of respect for the victims.
"Words cannot express the horror that I feel. I cannot begin to truly understand the pain and grief of the victims and their loved ones, but my heart goes out to them," Bale said in a statement.
The horrific attack in Aurora, Colorado, has revived the debate over gun control in the United States, and drew condemnation by President Barack Obama and his Republican White House rival Mitt Romney.
Bomb experts were finally inching their way into the home of James Holmes, the 24-year-old who allegedly opened fire on a packed midnight screening of the third and final "Dark Knight" movie, also injuring 58 others.
A small boom from a "controlled detonation" could be heard by reporters outside the apartment block and pieces of debris were blown out of one of the windows through which police have been assessing the booby-trap set-up inside.
Aurora police chief Dan Oates did nothing to hide his anger at what the authorities found inside the apartment.
"Make no mistake, this apartment was designed to kill whoever entered it. And who was most likely to enter that location after he planned and executed this horrific crime? It was going to be a police officer," he said.
"And if you think we're angry, we sure as hell are angry, about what has happened to our city, what has happened to these wonderful people who live here, and also what he threatened to do to one of our officers."
The 12 fatalities from the midnight theater rampage included 6-year-old Veronica Moser-Sullivan, according to the Arapahoe County Coroner's Office, which said they all died of gunshot wounds.
"She was beautiful and innocent," the girl's great aunt Annie Dalton told The Denver Post, recalling how the blonde Moser-Sullivan "loved to dress up and read, and was doing well at school."
The child's mother Ashley Moser, 25, was shot in the neck and abdomen and is in critical condition at Aurora Medical Center, drifting in and out of consciousness, and is unaware that her daughter is dead, the Denver Post said.
Many of those wounded in the mass shooting will suffer long-term consequences, a doctor said Saturday.
It "pretty much runs the gamut of multiple gunshots," said Bob Snyder of the Medical Center of Aurora, where four patients remain in intensive care, two in critical condition.
Late Friday the town near Denver gathered for two vigils as it emerged that Holmes bought more than 6,000 rounds of ammunition on the Internet, and four guns, in the two months before the rampage.
The shooter, dressed in black and wearing body armor and a gas mask, burst into the movie theater barely 20 minutes into the midnight screening early Friday, throwing two tear-gas type devices before opening fire with several weapons.
Police arrested Holmes by his car at the rear of the theater. He offered no resistance.
New York City Police Commissioner Raymond Kelly said Friday that the gunman "clearly looks like a deranged individual."
"He has his hair painted red. He said he was the Joker, obviously the enemy of Batman," Kelly told reporters.
Aurora police chief Oates did not comment, but said Saturday that Holmes had received a large number of packages over the past four months and "this begins to explain how he got all the magazines and the ammunition" used in the attack.
"We also think it begins to explain some of the materials that he had in his apartment," he said. "What we're seeing here is evidence of, I think, some calculation and deliberation," he said.
Oates flatly declined to speculate on any motive for Holmes, who is to make his first court appearance on Monday. "We're not going to talk about motive," he said.
Oates said that out of "an abundance of caution," bomb-sniffing dogs had made a sweep of buildings at the University of Colorado medical school, which Holmes attended until last month, but did not find anything unusual
Holmes had no criminal record aside from a citation for speeding in October 2011, according to police.
Cinemas in New York tightened security at Batman showings, and the AMC theater chain announced a ban on face masks and fake weapons, while a French premiere was canceled on Friday.
Aurora is 20 miles (32 kilometers) from the scene of the 1999 Columbine High School massacre, in which two students shot dead 13 people before committing suicide.