DENVER >> Jury selection was set to begin today in the long-delayed trial of a man charged with murdering 10 people at a Colorado supermarket in 2021, a case in which the suspect was ruled mentally unfit to face prosecution before pleading not guilty by reason of insanity.

The outcome hinges on whether the defense can convince jurors that Ahmad Al Aliwi Alissa, 25, was so mentally ill at the time of the mass shooting that he failed to comprehend the difference between right and wrong and thus should not be held legally responsible for the killings.

The basic facts of the case are not in dispute. Alissa stormed a King Soopers grocery store in Boulder, about 28 miles northwest of Denver, on March 22, 2021, armed with a legally purchased Ruger AR-556 pistol, which resembles an AR-15-style rifle.

Police say he killed two people in the store’s parking lot before shooting eight others to death inside the supermarket. Among those killed were a police officer responding to the scene.

The shooting spree ended when a police officer shot Alissa in the leg, leading the gunman, wearing only his underwear, to surrender. He has remained in custody since the day of the shooting.

Alissa is charged with 10 counts of first-degree murder, in addition to dozens of counts of attempted murder, assault and weapons offenses stemming from the rampage.

A conviction would carry an automatic sentence of life in prison without parole. There is no death penalty in Colorado.

The case against Alissa stalled after he underwent a court-ordered psychiatric evaluation and was diagnosed with schizophrenia in late 2021. Boulder District Court Judge Ingrid Bakke, relying on the conclusions of state psychologists, then deemed him incompetent to stand trial.

In November 2023, Bakke found that the defendant’s mental condition had improved sufficiently under psychiatric treatment to rule him restored to competency, allowing the prosecution to move forward.

Competence is a legal determination that weighs whether criminal defendants understand the charges against them and can meaningfully assist in their own defense. An insanity plea relates instead to the defendant’s mental status at the time of the alleged crime.

Grim details of the killings emerged during his plea hearing last year, when a Boulder homicide detective testified that Alissa shot one man in the back, then pursued the victim as he tried to crawl away and fatally shot him again. The detective also testified the suspect shot and wounded a woman, then fired multiple additional rounds at her as she curled up in a fetal position, killing her.

All the victims struck by gunfire died of their wounds, authorities said.

A precise motive for the killing spree has not been suggested by prosecutors, though according to a psychologist who treated the gunman at a state mental hospital, Alissa had said he wanted to “commit suicide by cop.”