President Barack Obama paid emotional tribute to the victims and survivors of the Aurora cinema massacre, as the shaken US town held a tearful vigil for the 12 dead filmgoers.

Obama, making a visit to the stricken Colorado town, said he shed tears with relatives of those who died as the community struggles to recover from Friday's shooting at a screening of the latest Batman movie, which also left 58 injured.

"I confessed to them that words are always inadequate in these types of situations," he said as thousands gathered for a vigil outside the municipal center in Aurora, just outside Denver.

Speaking after visiting with families in hospital, he said he "had the chance to give folks some hugs, and to shed some tears, but also to share some laughs" as families remembered the "wonderful" lives of their loved ones.

The alleged gunman, 24-year-old James Holmes, is accused of bursting into a packed midnight screening of "The Dark Knight Rises" early Friday, throwing two canisters of noxious gas into the crowd, and then shooting at random.

The victims included a six-year-old girl, Veronica Moser-Sullivan, whose mother was also critically wounded.

Shortly after Obama's speech, thousands of locals applauded as police officers, army and other officials came towards a stage for the start of the vigil.

"While our hearts are broken, our community is not," Aurora Mayor Steve Hogan told the crowds, which included many people in tears.

Colorado Governor John Hickenlooper drew applause when he refused to mention Holmes by name, referring to him only as "suspect A" and insisting that the priority should be to remember the 12 victims.

He then read out their names, after which the crowd said, "We will remember."

Police revealed on Sunday that they had found Holmes's 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, who is due to make his first court appearance on Monday, is being held in solitary confinement for his own protection, a police spokeswoman said.

It was also reported that Holmes had applied to join a private gun club a few weeks before the shooting, but his paperwork appeared suspicious and he was not approved.

The owner of Lead Valley Range, Glenn Rotkovich, telephoned Holmes shortly after receiving his application on June 25, and was greeted by a "bizarre and creepy" voicemail greeting.

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

Aurora is located 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.

City police chief Dan Oates praised his men for spotting Holmes as a suspect in the "chaos" that followed the shooting, as officers could have mistaken him for an arriving SWAT officer, because of his full body armor.

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 the issue.

"This really is an enormous problem for the country, and it's up to these two presidential candidates," he said.

Meanwhile actress Anne Hathaway, who plays Catwomam, became the latest cast member to voice her shock at the killings, saying: "My heart aches and breaks for the lives taken and altered by this unfathomably senseless act."

Bomb experts cleared Holmes's apartment of all major explosives threats on Saturday.

CNN and the LA Times cited police sources as saying that a Batman mask and poster were among the contents recovered from the apartment. The Aurora Police Department declined to confirm or deny the report.

Obama ended his remarks by recounting one particular tale of heroism he was told by 19-year-old Allie Young and her friend Stephanie Davies.

He told how, when the gunman threw gas canisters, one landed a few feet away from the pair. Young stood up to warn people, and was immediately shot in the neck, "and started squirting blood."

"Apparently as she dropped down on the floor, Stephanie, 21 years old, had the presence of mind to drop down on the ground with her, pull her out of the aisle, place her fingers over where Allie had been wounded and applied pressure the entire time while the gunman was still shooting."

Although Young told her friend to run, Davies instead called 911 on her cellphone, with the other hand staunching the blood, all while the gunman continued to fire.

After SWAT teams arrived, Davies helped carry her friend across two parking lots to a waiting ambulance.

"And because of Stephanie's timely actions, I just had a conversation with Allie downstairs and she is going to be fine," Obama said.