Americans got a first look at presumed gunman James Holmes at a brief court hearing Monday, but remained perplexed over what triggered his alleged movie house shooting frenzy that took the lives of 12 people.
His hair dyed orange, eyes staring out blankly, Holmes made a bizarre first appearance in court, three days after the rampage that also wounded 58.
The deadly shooting occurred shortly after midnight Friday at a movie theater in Aurora, Colorado, outside Denver, as moviegoers packed the first screening of the latest Batman film, "The Dark Knight Rises."
Wearing a maroon prison jumpsuit, the 24-year-old graduate school dropout didn't speak as lawyers read out a list of accusations during the short procedural hearing at Arapahoe County District Court in the town of Centennial.
Holmes, a former PhD candidate in neuroscience, appeared unable to follow proceedings as his head bobbed up and down and he alternated between staring out wild-eyed and closing his eyes shut as if drugged or in a daze.
It was not known if he was on medication and there was no indication when the young man accused of one of America's worst-ever mass shootings might undergo psychiatric evaluation.
Holmes gave himself up outside the cinema, still clad in the body armor witnesses described the gunman as wearing.
He is expected to face 12 murder charges, 58 attempted murder charges for those he wounded, and additional charges related to his booby-trapped apartment.
Holmes is being held in solitary confinement in the Arapahoe County jail, with no bail allowed. He is to make a second court appearance next Monday when he will enter a plea.
A first year doctoral candidate, Holmes unexpectedly dropped out of the University of Colorado last month after failing part of his end-of-year exams.
Graduate school dean Barry Shur said at a press conference Monday that like all candidates to the elite program, Holmes came with "excellent academic credentials," and university officials were in shock over the charges against the former student.
Prosecutors expect weeks of consultations with families of the victims before deciding whether or not to seek the death penalty for Holmes, who would be the first person executed in Colorado since 1997.
"We will want to get their input before we make any decision on that," said Arapahoe county district attorney Carol Chambers.
The gunman emerged from a fire exit on Friday shortly after the film began and threw two canisters of noxious gas into the auditorium.
After firing one round directly into the air with a pump-action shotgun, he began shooting people at random with a military-style assault rifle that could dispatch 50 to 60 rounds a minute, witnesses said.
Authorities said Holmes had painted his hair reddish orange and claimed he was the Joker, Batman's sworn enemy in the comic book series that inspired the movie.
According to reports and at least one witness, he might have killed more people had his assault rifle not jammed.
Police said Sunday they had found Holmes's computer inside his booby-trapped apartment -- rigged to kill anyone who entered -- which could provide crucial details about how he planned and executed the attack.
Calls to re-examine US gun laws mounted as it emerged that Holmes bought his four weapons legally, as well as thousands of rounds of ammunition on the Internet.
Over eight weeks he stocked up on 6,300 rounds of ammunition: 3,000 for his .233 semi-automatic AR-15 rifle, another 3,000 for his two Glock pistols, and 300 cartridges for his pump-action shotgun.
New York Mayor Michael Bloomberg late Monday urged President Barack Obama and his Republican rival for the White House Mitt Romney to make the bid to clamp down on the rampant proliferation of firearms a talking point of their respective campaigns.
"Since 48,000 people will be murdered with guns in... the next four-year presidential term, I would argue it's a substantial problem and that they have an obligation to tell the public before the public goes to the voting booth what they will do," Bloomberg told CNN.
Obama paid emotional tribute to the victims and survivors of the Aurora cinema massacre as he visited the town on Sunday.
At an event for US veterans in Reno, Nevada, he repeated particular condolences for four people killed who had served in the military.
"These young patriots were willing to serve in faraway lands, yet they were taken from us here at home," he said.
As campaigning ahead of the November election geared up again, his rival Romney stressed that now was not the time to discuss new gun legislation.
"Our challenge is not the laws, our challenge is people who, obviously, are distracted from reality and do unthinkable, unimaginable, inexplicable things," Romney said.