James Holmes, the former PhD-student accused of killing 12 people in Colorado when he opened fire in a cinema during a midnight screening of Batman, intends to plead not guilty by reason of insanity, his lawyers have said.
Lawyers acting for the 25-year-old said they would ask for the change of plea at a hearing scheduled next Monday.
If the judge accepts the new plea, Mr Holmes is likely to be moved to a psychiatric hospital where doctors will determine whether he was insane at the time of the attack. A jury could still find him guilty despite a medical finding of insanity.
Colorado law defines insanity as the inability to distinguish right from wrong, caused by a diseased or defective mind. Mr Holmes's lawyers have said at hearings and in court documents that they believe the former student is mentally ill. He was being seen by a psychiatrist before the shooting.
The trial had been scheduled for August, but a judge has pushed it back to February 2014. It was unclear if the new plea will further delay the case.
A judge previously entered a not guilty plea after the defence said Mr Holmes was not ready to plead. Prosecutors have previously said that they will seek the death penalty against the man accused of killing 12 and injuring 70 in a shooting spree at the Century Aurora 16 which spurred new gun control laws in Colorado. Earlier this year, prosecutors rejected an earlier offer from Mr Holmes's lawyers to plead guilty in order to avoid execution.
Mr Holmes is accused of stockpiling weapons and ammunition for his assault on a packed midnight screening of The Dark Knight Rises in Aurora, Colorado on July 20 last year and booby-trapped his apartment to explode and distract any police who responded.
The attack was repeatedly cited by gun control advocates who pushed a hotly contested package through the Colorado state legislature. The bills, which include a ban on the sort of high-capacity magazines that Holmes allegedly sprayed dozens of bullets in a matter of seconds, will come into effect on July 1.