A Colorado judge entered a plea of not guilty on behalf of James Holmes, whose attorney said he was not ready to enter one in the Aurora shooting case.
The judge thus entered a not guilty plea for him and said he could change the plea to not guilty by reason of insanity, the Associated Press reports.
James Holmes, who faces 166 counts of murder, manslaughter and other crimes for the July 2012 massacre, sat silent, but alert, at the hearing.
He alternately appeared to look at the judge and stare into space.
Jailed for eight months now, the 25-year-old was reportedly restrained in a psychiatric ward for several days last fall out of fear he might harm himself.
To be found not guilty by reason of insanity, Holmes has to prove he did not know right from wrong when he committed the crime of which he is accused.
Prosecutors say Holmes planned the massacre well in advance, ordering arms and ammunition through the internet and dressing in paramilitary gear.
To make matters even worse, police also found explosives in his apartment that had reportedly been rigged to go off when authorities entered.
Holmes had no connection to his victims, and unlike Newtown shooter Adam Lanza, or Columbine shooters Eric Harris and Dylan Klebold, did not commit suicide.
He has been compared to Jared Loughner, who opened fire outside a Tucson supermarket in 2011, killing 6 and wounding 13 others, including Rep. Gabrielle Giffords.
Loughner, a diagnosed schizophrenic, was initially ruled not competent to stand trial, but after more than a year of treatment inside a federal prison, pleaded guilty.
He was sentenced to life without parole.
The D.A. will make an announcement on April 1 about whether he intends to seek the death penalty for Holmes, whose defense asked for more time to prepare.