The man accused of going on a deadly shooting rampage at the opening of the new Batman movie appeared Monday in court for the first time.
James Holmes, 24, who is accused of killing 12 people and wounding 58 others inside a packed movie theater in Aurora, Colo., will be formally charged next Monday. He is being held without bond.
Holmes, who did not speak, sat in a maroon jailhouse jumpsuit as the judge advised him of the case. He appeared wide-eyed with bright reddish orange hair.
Holmes has been held in solitary confinement at an Arapahoe County detention facility since Friday. He is being held on suspicion of first-degree murder, and he could also face additional counts of aggravated assault and weapons violations.
Authorities say the former graduate student is refusing to cooperate and it could take months to learn what prompted the horrific attack on moviegoers at a midnight screening of the latest Batman film.
During the attack, Holmes allegedly set off gas canisters and used a semiautomatic rifle, a shotgun and a pistol to open fire, police said.
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The semiautomatic assault rifle jammed during the attack, forcing the gunman to switch to another gun with less firepower, a federal law enforcement official told The Associated Press. That malfunction and weapons switch might have saved some lives.
District Attorney Carol Chambers said Monday that her office is considering pursuing the death penalty against Holmes. She said a decision will be made in consultation with victims' families.
"That’s a very long process that impacts their lives for years," Chambers said of the victims' families during a press conference Monday. She said that decision "could be weeks or months away."
"It's still a very active and ongoing investigation," Chambers said. "There's no such thing as a slam dunk case."
"We will ask the court to continue holding him without bond," she added.
Investigators searching Holmes' apartment on Sunday found multiple Batman-related items. A law enforcement source confirmed to Fox News that investigators seized a Batman poster and a mask connected to the Batman movies from Holmes' apartment.
A law enforcement official told The Associated Press the mask found was a Batman mask. Investigators also took other items from the apartment, including a computer tower.
A law enforcement source said in addition to multiple booby traps and ammunition, officials also removed 10 gallons of gas that appeared ready to explode.
"The idea was ... he wanted to burn this place down," the source said. "And the gas would have made that fast."
Agents said they believe the person who opened the door would have been killed, setting off a fire storm that could have trapped people inside the building in the middle of the night.
A student living two floors below Holmes told Fox News that he only saw Holmes twice inside the building. He said Holmes was quiet and kept to himself.
Police have said Holmes began buying guns at Denver-area stores nearly two months before the shooting and that he received at least 50 packages in four months at his home and at school. He recently purchased 6,000 rounds of ammunition over the Internet, Aurora Police Chief Dan Oates said.
Officials at the University of Colorado -- where Holmes was a doctoral student until recently dropping out -- are investigating whether he used his position in a graduate program to collect hazardous materials. It remained unclear whether Holmes' professors and other students at his 35-student Ph.D. program noticed anything unusual about his behavior.
Holmes' reasons for quitting the program in June -- just a year into the five- to seven-year program -- also remained a mystery.
Holmes recently took an intense, three-part oral exam that marks the end of the first year. Those who do well on the test continue with their studies and shift to full-time research, while those who do not are required to meet with advisers to discuss their options, including retaking the exam. University officials would not say if he passed, citing privacy concerns.
The university said Holmes gave no reason for his withdrawal, a decision he made in June.
Holmes was not allowed access to the institution after his withdrawal, which was "standard operating procedure" because he was no longer affiliated with the school, a school official said.
Fox News' Adam Housley, Griff Jenkins and the Associated Press contributed to this report.