CENTENNIAL, Colo. -- The accused gunman in last year's Colorado theatre shooting won't have to enter a plea until March, as the possibility grew Friday that his lawyers would request a mental health examination.

A judge granted the request by James Holmes' lawyers to delay his arraignment until March 12. The decision came a day after the judge ruled that Holmes should stand trial for one of the country's worst mass shootings. The attack left 12 dead and 70 wounded, and Holmes is charged with multiple counts of first-degree murder and attempted murder and could face the death penalty.

Defence lawyers didn't give a reason for the plea delay.

A majority of the families of the victims objected, and an unidentified man in the courtroom yelled, "Rot in hell, Holmes" at the end of the hearing.

Lawyers for the 25-year-old might want to seek a mental health evaluation by a doctor of their choosing. The lawyers have said Holmes is mentally ill, raising the possibility of an insanity defence.

Prosecutors this week made a graphic case to bring Holmes to trial.

Holmes is accused of entering the theatre during a midnight showing of the latest "Batman" movie, wearing body armour, and spraying the crowd with bullets. Police say he also rigged his apartment to explode and distract officers from the theatre, but the explosives were not triggered and were taken apart by authorities.

Prosecutors presented self-portraits that Holmes took hours before the July attack, sometimes smiling and sometimes with a pistol. Another photo showed weapons, ammunition and body armour spread out on his bed.

Witnesses testified that Holmes had two semi-automatic pistols, a shotgun, a semi-automatic rifle, 6,200 rounds of ammunition and high-capacity magazines that allow a shooter to fire more rounds without stopping to reload.

Ultimately, Holmes is widely expected to plead not guilty or -- more likely -- not guilty by reason of insanity.

If found not guilty by reason of insanity, Holmes would be committed to the state mental hospital for treatment. His case would be reviewed every six months. He conceivably could be released if he is deemed no longer insane.

"Insanity is what this case is going to turn on," said Denver criminal defence attorney Dan Recht. "This is not a whodunit case."