US President Barack Obama headed to Colorado on Sunday to meet victims of the cinema shooting massacre, as Aurora residents flocked to church services in memory of the 12 slain moviegoers.

Another 58 people were injured, nearly all of them shot, when the gunman, dressed in black and wearing body armor and a gas mask, burst into the packed Batman premiere "The Dark Knight Rises" shortly after midnight on Friday.

The alleged gunman, 24-year-old James Holmes, emerged from the fire exit, threw two canisters of noxious gas into the crowd, fired one shot up in the air and then began shooting randomly into the panicked crowd.

Police revealed Sunday that they found Holmes' computer inside his booby-trapped apartment, which could provide crucial details about how he planned and executed the attack, reportedly over a number of months.

Holmes is being held in solitary confinement for his own protection, a police spokeswoman said.

The town's churches were packed Sunday morning, with some people sobbing -- many church-goers said they knew someone involved in the shooting.

"My niece was in the theater but she was lucky to get out," said 15-year-old student Keshala Ferguson, among a capacity 500-strong congregation at the Queen of Peace Catholic church.

"It was nerve-wracking for her mom, but she's OK. The mass was amazing. Everybody needs to pray."

Calls for another look at America's gun laws are mounting in the aftermath of the tragedy as it emerged that the alleged shooter bought his four weapons legally, as well as thousands of rounds of ammunition on the Internet.

Police on Saturday entered the gunman's apartment and revealed the names of the 12 fatalities, including a six-year-old girl whose mother was among those seriously injured.

Aurora, a town outside Denver, Colorado, 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.

Police chief Dan Oates also revealed Sunday that Holmes could have been mistaken for an arriving SWAT officer, because of his full body armor, but praised his men for spotting him as a suspect.

"I can't tell you in that chaos it is quite reasonable that an officer might have confused him for a SWAT officer, a heavily armed officer who was responding to the scene," he told CBS talk show "Face the Nation."

The president will meet with families and victims, and is planning to go to a hospital, Hickenlooper said, though it is unlikely that he will stay for a community vigil scheduled in Aurora for the early evening.

New York Mayor Michael Bloomberg -- one of the few high-ranking US politicians that openly favors gun control -- demanded Sunday that both Obama and his Republican presidential rival, Mitt Romney, take action on gun control.

"This really is an enormous problem for the country, and it's up to these two presidential candidates. They want to lead this country, and they've said things before that they're in favor of banning things like assault weapons," Bloomberg said on the CBS show "Face the Nation."

"Where are they now and why don't they stand up?" asked Bloomberg. "If they want our votes, they'd better."

Meanwhile actress Anne Hathaway became the latest cast member to voice her shock at the killings, after the studio behind the new Batman movie said it was withholding box office data out of respect for the victims.

"My heart aches and breaks for the lives taken and altered by this unfathomably senseless act. I am at a loss for words how to express my sorrow," said Hathaway, who plays Catwoman.

Bomb experts spent Saturday inching their way into Holmes's apartment. A small boom from a controlled detonation blew out a few pieces of debris, and a short time later police announced they had defused all major threats.

Early Sunday police dismissed media reports that another person, a fellow medical PhD student, had helped Holmes in his killing spree and had called the police, threatening more violence if Holmes was not released.

The 12 fatalities from the midnight theater rampage included six-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 child "loved to dress up and read, and was doing well at school."

Authorities said Holmes bought more than 6,000 rounds of ammunition online, as well as four guns in the two months before the rampage.

Police arrested Holmes by his car at the rear of the theater after the shooting. He offered no resistance.

New York City Police Commissioner Raymond Kelly said Holmes had painted his hair red and claimed he was the Joker, Batman's sworn enemy. The suspected gunman "clearly looks like a deranged individual," he added.

Oates declined to speculate on any motive for Holmes, who is due to make his first court appearance on Monday.