Batman massacre gunman James Holmes has appeared in court in Colorado with bright orange dyed hair.
Holmes sat wide-eyed and appeared dazed as the judge in Denver advised him of his legal rights.
The court heard he will be formally charged next Monday with the murders of 12 people at the Batman film premiere.
The 24-year-old former graduate student is refusing to cooperate with police, and it could take months to learn what prompted Friday's attack on moviegoers at the midnight screening.
Investigators say they found a Batman mask inside Holmes' booby-trapped apartment.
Holmes has been held in solitary confinement since Friday. Prosecutors say they may consider the death penalty but will make that decision after consulting with victim's families.
Holmes began buying guns nearly two months before the shooting and recently bought 6,000 rounds of ammunition over the internet, police chief Dan Oates said.
During the attack, Holmes set off gas canisters and used a semi-automatic rifle, a shotgun and a pistol.
The assault rifle jammed during the attack, forcing the gunman to switch to another gun with less firepower, which may well have saved more lives.
Holmes' apartment was filled with trip wires, explosive devices and unknown liquids, requiring police, FBI officials and bomb squad technicians to evacuate surrounding buildings while spending most of Saturday disabling the booby traps.
Investigators have said they found a Batman mask inside the apartment.
As authorities rushed to piece together Holmes' background, the owner of a gun range said that Holmes applied to join the club last month but never became a member because of his behaviour and a "bizarre" message on his voice mail.
When Lead Valley Range owner Glenn Rotkovich called to invite Holmes to a mandatory interview, he said he heard a message on Holmes' voice mail that was "guttural, freakish at best."
He told his staff to watch out for Holmes and not to accept him into the club.
The University of Colorado Anschutz Medical Campus is looking into whether Holmes, a former doctoral student in neuroscience, used his position in a graduate programme to collect hazardous materials.
Holmes' reasons for quitting the doctoral program in June remained a mystery. He recently took an intense, three-part oral exam that marks the end of the first year. University officials would not say if he passed.
Ritchie Duong, a friend who has known Holmes for more than a decade, told the Los Angeles Times that he last saw Holmes in December and he seemed fine.
Academics came easily to Holmes, Mr Duong said. "I had one college class with him, and he didn't even have to take notes or anything."
The family's pastor recalled a shy boy who was driven to succeed academically.
"He wasn't an extrovert at all. If there was any conversation, it would be because I initiated it, not because he did," said Jerald Borgie, who last spoke with Holmes about six years ago.
Sunday was a day for healing and remembrance in Aurora. Several thousand people attended a prayer vigil, and President Barack Obama visited families of the victims.