A US judge ruled on Monday that accused movie theater shooter James Holmes could plead not guilty by insanity, but said he would not yet formally accept the change of plea.
Judge Carlos Samour set a new hearing for May 31 for lawyers for Holmes, accused of killing 12 people in a Colorado cinema last year, to enter the change of plea.
The trial judge had entered a straight not guilty plea on Holmes' behalf in March. At that time, his lawyers said they were not yet ready to enter a plea for Holmes, also accused of injuring another 70 people in the incident.
The July 20 massacre took place at a midnight screening of the Batman movie "The Dark Knight Rises" in the Colorado town of Aurora, outside Denver, reviving America's long-running debate about gun control.
Witnesses said Holmes threw smoke bomb-type devices before opening fire in the theater with weapons including an AR-15 military-style rifle, a 12-gauge shotgun and a .40-caliber pistol.
When Holmes first appeared in court last year, he had bright orange hair and looked befuddled. He has since let his hair color grow out and now has curly brown hair and a beard.