DENVER, Colorado: The alleged gunman in the Colorado cinema massacre of 12 people is due to be arraigned for trial Friday, after testimony this week gave harrowing new details of the slaughter.

James Holmes, 25, is accused of opening fire at a a midnight screening of the latest Batman movie in a theater in Aurora, Colorado on July 20, killing a dozen people and injuring at least 58 more.

At the hearing, he will hear each of the 166 charges he faces, which include murder in the first degree for the 12 people who died, attempted murder for the injured, as well as possession of explosives or incendiary devices.

He will also enter a plea.

Over three days earlier this week, prosecutors called witnesses who gave chilling accounts of the slaughter, and played 911 emergency calls in which the chaos and loud gunshot booms could be clearly heard.

Holmes's lawyers had been expected to present witnesses to bolster a case that he may be mentally unfit to stand trial.

But in the end they announced they would not, and Judge William Sylvester ruled that prosecutors had established there was "probable cause" to believe the defendant committed the crimes.

Shortly before the judge's trial order, Holmes' lawyers filed a motion for Friday's court appearance to remain merely a status hearing, rather than an arraignment, in which he is formally charged.

But Sylvester said the hearing, scheduled for 9:00 am (1600 GMT) Friday, "is hereby converted to an arraignment."

"The court orders that Defendant shall be bound over for trial on all counts," he wrote in a 61-page ruling posted online.

Witnesses said Holmes threw smoke bomb-type devices before opening fire randomly with weapons including an AR-15 military-style rifle, a 12-gauge shotgun and a .40-caliber pistol.

The judge also dismissed suggestions that Holmes was mentally unfit to stand trial.

"The court finds... that there is probable cause to believe that Defendant had the requisite mental state... necessary to commit the crime of first degree murder after deliberation," he wrote.

During this week's preliminary hearings, the prosecution presented evidence that Holmes had planned the attack well in advance.

It included photos found on his iPhone suggesting he had surveyed the cinema weeks before the shootings. There were several images showing him posing with guns and explosive devices hours before the massacre.

He had also made at least 16 purchases from May to July 2012, including four firearms, incendiary devices and almost 6,300 rounds of ammunition, the court heard.

Before this week's hearings, there had been speculation that Holmes' lawyers could seek a plea agreement under which he would admit guilt in return for avoiding the death penalty, for example.

The Aurora massacre revived the perennial US debate over gun control -- an issue re-ignited even more intensely by last month's shooting of 20 young children at a Connecticut elementary school.