A judge has ruled that there is enough evidence for James Holmes to face trial on charges that he killed 12 people and injured 70 others in a Colorado cinema last summer.
Judge William Sylvester said prosecutors have established probable cause to proceed with 166 felony counts, including murder and attempted murder.
Holmes is due to be arraigned later, but his defence lawyers filed papers saying he is not ready to enter a plea. They are likely to appear in court to ask for the arraignment to be delayed.
Defence lawyers did not explain why they are not ready for arraignment. Their filing also objected to media requests to bring cameras into the courtroom. Other than during his brief initial appearance in July, cameras have been barred from court during Holmes' case.
Mr Sylvester's ruling came after a three-day hearing earlier this week, in which prosecutors laid out their case against Holmes, 25.
A succession of police and federal agents testified that Holmes spent weeks amassing guns and ammunition, concocted explosives to booby-trap his apartment and scouted the cinema where he would allegedly unleash a horrific attack on hundreds of terrified people.
The officers also described a hellish scene inside the cinema on July 20, when 12 people were shot dead before their families and friends' eyes and scores of others were wounded amid a din of gunshots, screams and the blaring soundtrack of The Dark Knight Rises.
Holmes' lawyers called no witnesses and cross-examined only a few of those summoned by prosecutors during the hearing. But they pointedly raised the issue of Holmes' sanity at strategic moments, possibly foreshadowing a defence that some believe is his best hope to avoid the death penalty.
"You're aware that people can be found not guilty on the grounds of insanity?" defence lawyer Daniel King asked one witness.
The preliminary hearing, which ended on Wednesday, was designed to determine whether the prosecutors' case is strong enough to put Holmes on trial. Holmes' lawyers have not said if he will plead not guilty by reason of insanity, but since his arrest outside the cinema in the Denver suburb of Aurora immediately after the shootings, they have portrayed him as a man with serious mental problems prone to bizarre behaviour.