Prosecutors were expected to charge James Holmes with multiple murder Monday after 12 people were shot dead at a Batman screening in Colorado, one of America's worst ever mass shootings.
Holmes could face up to two counts, including first-degree murder, for each person he allegedly killed. He could also be charged with the attempted murder of all those inside the cinema in Aurora, near Denver, not just people he shot.
Prosecutors have said it will be several weeks before a decision is made on whether or not to seek the death penalty. Only one person has been executed in Colorado since capital punishment was reinstated in 1976.
The few journalists allowed to attend the 9:30 am (1530 GMT) hearing will be watching to see if there is a repeat of the 24-year-old's bizarre behavior during his first court appearance a week ago.
Under a mop of brightly-dyed orange and red hair, he stared out wild-eyed at times but appeared almost sleepy at others, appearing unable to keep up with the proceedings.
Holmes gained access to the movie theater via a fire exit shortly after the start of the latest Batman film, "The Dark Knight Rises," and threw two canisters of noxious gas into the auditorium, witnesses and police said.
After firing into the air with a pump-action shotgun, the former graduate neuroscience student allegedly began shooting people at random with a military-style assault rifle capable of firing 50 to 60 rounds a minute.
The 12 victims included six-year-old Veronica Moser-Sullivan. The girl's mother, among 58 moviegoers wounded, is in critical condition after being shot in the neck and stomach and has since lost her unborn child.
Prosecutors have been battling defense lawyers over a package Holmes sent to his psychiatrist at the University of Colorado portending the midnight massacre on July 20 at the cinema in Aurora.
Attorneys for Holmes disclosed on Friday that he had been a patient of University of Colorado psychiatrist Lynne Fenton as they sought to gain access to a package he had mailed to her prior to the massacre.
Holmes's lawyers are accusing prosecutors of leaking to the media the existence of the package - reportedly containing macabre plans, including drawings of a stick-figure gunman mowing down victims.
"The government's disclosure of this confidential and privileged information has placed Mr Holmes's constitutional rights to due process and a fair trial by an impartial jury in serious jeopardy," his attorneys wrote.
There has been speculation that stress over failing an important oral exam may have been the trigger that caused Holmes, a promising neuroscience student who had won a prestigious government grant, to become unhinged.
ABC News' affiliate in Denver, KMGH-TV, reported that Holmes purchased a high-powered rifle on June 7, hours after failing the key oral test. Three days later, he dropped out of his university program.
Although the shooting has triggered some soul searching in the United States there has been no concerted political will to address the toxic gun law issue, especially four months out from a presidential election.
As of Sunday, 10 patients from the theater shooting remained hospitalized - four of them in critical condition.
Holmes is said to have stocked up on more than 6000 rounds of ammunition over the Internet and to have bought four weapons in local gun shops.