The judge also granted prosecutors access to a hotly contested notebook that Holmes sent to a psychiatrist shortly before the July 20 rampage, which left 12 people dead and 70 injured in a bloody, bullet-riddled movie theatre in suburban Denver.
Taken together, the three developments marked a major step forward in the 10-month-old case, which at times has inched along through thickets of legal arguments or veered off on tangents.
Holmes faces more than 160 counts of murder and attempted murder, and prosecutors are seeking the death penalty.
He will now be examined by the Colorado Mental Health Institute in Pueblo, but it's not certain when the evaluation will begin or how long it will take. Hospital officials have said that before they meet with Holmes, they want to review evidence in the case, which prosecutors said totals nearly 40,000 pages.
Judge Carlos Samour Jr. set a tentative date of Aug. 2 for the exam to be complete but said he would push that back if hospital officials request more time. Samour indicated he still hopes to begin Holmes' trial in February.
Holmes, 25, shuffled into court with his wrists and ankles shackled, wearing a long, bushy beard and dark, curly hair that was slicked back.
Samour read Holmes a five-page list of consequences of the insanity plea and asked if he had any questions.
"No," Holmes answered in a clear, firm voice. It was only the second time since his arrest that he has spoken in court, other than occasional whispered exchanges with his attorneys.
The findings of the mental evaluation will become evidence in Homes' trial, but they are not the final word on whether he was legally insane at the time of the shootings. The jurors will determine that.
If their verdict is not guilty by reason of insanity, Holmes would be committed to the Mental Health Institute indefinitely. He could theoretically be released one day if doctors determine his sanity has been restored, but that is considered unlikely.
If their verdict is guilty, jurors would then decide whether Holmes will be executed or spend the rest of his life in prison without the possibility of parole.
Colorado law defines insanity as the inability to distinguish right from wrong caused by a diseased or defective mind.
Marcus Weaver, who was wounded and lost his friend Rebecca Wingo in the shooting, doesn't believe Holmes is insane but is grateful the case is moving forward.
"As we've seen evidence and seen the case unfold, it's become more evident that Mr. Holmes did what he did, and it had nothing to do with his mental state," he said.
The insanity plea is widely seen as Holmes' best chance of avoiding execution, but his lawyers delayed it for weeks, saying Colorado's laws on the insanity plea and the death penalty could work in combination to violate his constitutional rights.
The judge overruled their objections last week, but on Tuesday he conceded one point: Neither Holmes nor his lawyers had to sign a statement or say in court that they understood the five-page list of consequences of the insanity plea.
Samour originally planned to require Holmes and the defence to acknowledge they understood those consequences before he accepted the plea. But Samour said Tuesday he had determined that wasn't required by law.
Holmes needed Samour's approval to enter the insanity plea because a judge had entered a standard not guilty plea on Holmes' behalf in March.
Prosecutors first sought access to the notebook when its existence was made public days after the shooting. Holmes had mailed it to Dr. Lynn Fenton, a University of Colorado, Denver psychiatrist who had treated Holmes. Holmes had been a graduate student in neuroscience at the university.
The notebook's contents have never been officially made public, but media reports have said it contains drawings depicting violence.
The defence argued the notebook was protected by doctor-patient privilege. But Samour ruled Tuesday that under Colorado law, Holmes waived that privilege when he entered the insanity plea.
Prosecutors said Tuesday that in addition to reviewing the contents of the notebook, they would ask police to do unspecified "additional processing" of it.
Court officials also released nearly 100 pretrial motions Tuesday, most of them from the defence.
One signalled that Holmes will seek a change of venue because of pretrial publicity. Others challenged the admissibility of ballistics, handwriting and mountains of other evidence and demanded that prosecutors hand over as many as 2,000 pieces of physical evidence.
Holmes' lawyers appear to be trying to humanize their client, who made his first court appearances with a mop of dyed orange hair. They filed motions asking that he be allowed to appear before jurors in civilian clothes, instead of a jail uniform, and without shackles. They also asked that authorities ratchet back courthouse security, including armed guards on the roof.
Defence lawyers want Holmes' parents to be allowed to witness the entire trial in support of their son and not be sequestered like other possible witnesses.
Associated Press writer Nicholas Riccardi contributed to this report.
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