A masked gunman has shot dead at least 12 people and wounded 58 others at a showing of the new Batman movie "The Dark Knight Rises" in the US state of Colorado.
Police in the Denver suburb of Aurora said on Friday they had arrested a 24-year-old local man in a car park nearby in possession of a rifle, handgun and a knife.
James Holmes is currently in custody, being questioned by the police.
Speaking to Al Jazeera from Aurora, reporter Leanne Gregg said officials were scrambling for more information on Holmes.
"He is 24 years old. He recently filled out a rental form in which he described himself as 'easy going'. He's from the San Diego area and police are now speaking with members of his family to learn what might have led to the alleged attack."
"We were told by police that he gave himself up willingly," she added.
They arrested the alleged gunman following chaotic scenes at a movie theatre at a local mall on Friday.
James Holmes, 24, was a PhD student of neuroscience at the University of Colorado
He lived in an apartment in the north of Aurora, only eight kilometres from the cinema
He has no previous criminal record and is in police custody
"This is a horrific event," Aurora Police Chief Dan Oates told a news conference, saying there was no evidence of a second gunman.
He told the news briefing that 10 people were killed on site and the others were later reported dead in area hospitals.
Some of the injured were children, with the youngest a 3-month-old baby. Victims were being treated for chemical exposure apparently related to canisters thrown by the gunman.
As police were trying to gain access to Holmes apartment, Aurora Police Chief Daniel Oates said: "His apartment is booby-trapped.
"We are trying to determine how to disarm the flammable or explosive material. We could be here for hours or days.
"The pictures are fairly disturbing. It looks very sophisticated, how it's booby-trapped. It could be a very long wait."
Police revised down the death toll from 14 earlier. They said about 70 people, including the deceased, had been shot in the incident at the Century 16 multiplex cinema.
Dozens of police were at the scene, and the authorities evacuated the area while they checked if there was an explosive device in the area.
Denver's' KOA radio station said a figure in a gas mask had opened fire at the showing in a mall in the suburb of Aurora and set off a smoke or tear gas bomb.
"A man apparently appeared in a riot helmet in a bullet-proof vest from behind the scene," said Al Jazeera's John Hendren, reporting from Chicago. "According to witnesses he set off a smoke bomb and then began firing into the crowd. The suspect is now in custody.
'Mass casualty incident'
Police spokesman Frank Fania said a male suspect was arrested in the parking lot behind the theatre. "He did not resist, he did not put up a fight," he said.
The gunman "appeared at the front of the screen" in the theatre and started shooting, Fania said.
Fania said police received the first call about the shooting at 00:39 local time and responded within "a minute or two". Local hospitals were alerted to a "mass casualty incident".
A spokeswoman for Denver's Swedish Medical Center on Friday said three people had been admitted to that hospital with gunshot wounds and were in critical condition.
Another hospital, Denver Health, had received six wounded, one of whom was in critical condition, spokeswoman Kalena Wilkinson said.
Aurora is near the scene of the 1999 Columbine high school massacre, in which 13 people were shot dead and another 24 were wounded.
President Barack Obama on Friday said he was "shocked and saddened'' by a deadly mass shooting, and urged the nation to "come together as one American family".
Obama called the shooting "horrific and tragic'' and said his administration will do everything it can to support the people of Aurora.
According to the Hollywood Reporter plans for the film's red carpet premiere in the French capital Paris on Friday night were cancelled.