In their court filing, the attorneys said they intend to "tender a plea of not guilty by reason of insanity," The Denver Post reported. Under Colorado rules, they must show "good cause" for the change, with a ruling possible by next Monday.
Holmes, who had been a graduate student at the University of Colorado, allegedly killed 12 people and wounded 70 others during a midnight premiere of "The Dark Knight Rises" at the theater in Aurora.
If the judge grants the change of plea, the next step would be an independent psychiatric examination.
The filing was made a day after the Aurora City Council unanimously approved an outside review of police and fire response during the city's July 20 theater massacre. Despite objections from Arapahoe County District Attorney George Brauchler, the council voted Monday to hire, at a cost of $250,000, the TriData company to perform "after-action" analysis to document the shooting, the Post said.
"It's important to create a historical record of what occurred," said police Chief Dan Oates, who spoke in favor of the council's action.
Brauchler sent a letter to the council in February saying an independent investigation could hinder the prosecution of Holmes.