The man accused of killing 10 people at a Boulder, Colorado, supermarket in 2021 will stand trial, a judge ruled Tuesday, and he pleaded not guilty by reason of insanity.

Ahmad Al Aliwi Alissa, 24, is charged with murder and multiple counts of attempted murder for the deaths of customers, workers and a police officer who rushed in to help in the March 22, 2021, shooting at a King Soopers store in Boulder.

Trial proceedings had been delayed while his mental health was addressed. Alissa has schizophrenia, his lawyers previously said.

A plea of not guilty by reason of insanity means that defense attorneys may argue Alissa's mental health issues prevented him from being able to determine right from wrong at the time of the shooting.

10 killed in 2021 mass shooting

Alissa is accused of opening fire at about 2:30 p.m. outside and inside the store before finally surrendering when another officer shot and injured him. His attorneys have not disputed that he was the gunman.

Eric Talley, one of the the first Boulder police officers to respond to the frantic 911 calls, was killed, along with Rikki Olds, Denny Stong, Neven Stanisic, Tralona Bartkowiak, Teri Leiker, Suzanne Fountain, Kevin Mahoney, Lynn Murray and Jody Waters. Their ages ranged from 20 to 65.

Boulder Police Detective Sarah Cantu testified Tuesday that the gunman took just over a minute to kill most of his victims, and that all people he shot were killed. Cantu said Alissa pursued people who were moving and continued firing at them until they were dead.

Some of the charges he faces relate to endangering 26 other people there.

Robert Olds, whose 25-year-old niece Rikki olds was a front-end manager at the supermarket and was killed in the shooting, said he wanted justice for her.

“It’s the last fight, the last stand for my niece who can’t be here to do that herself because this guy murdered her,” Robert Olds said.

Defendant previously found competent to stand trial

In August, officials determined that Alissa was mentally competent to stand trial after receiving treatment, including being forcibly medicated, at a state facility.

The state's Department of Human Services found Alissa "does not currently have a mental disability or developmental disability" that would prevent him from understanding and participating in the court process, the Boulder County District Attorney's Office said in a statement at the time. 

The decision did not necessarily mean that Alissa no longer has schizophrenia, but that experts believed he had the ability to understand criminal proceedings and assist in his own defense. The determination is separate from the plea of not guilty by reason of insanity, which concerns the time of the shooting rather than the time of the trial.

The trial had been on hold since December 2021, when Alissa was found incompetent to stand trial but a judge said there was a reasonable chance he could be restored to competency through treatment.

Contributing: The Associated Press