The trial is expected to focus on the competence of the shooter in the 2021 Colorado supermarket massacre.

DENVER— The first person killed was a man sitting in a van after repairing a coffee machine at a supermarket in the college town of Boulder. In a span of just over a minute in 2021, nine more people were killed in and outside the store as a gunman targeted and chased people as they moved.

Survivors ran to the back of the store to avoid the bullets. For more than an hour, others hid on shelves, at checkouts and in offices.

Ahmad Al Aliwi Alissa, then 21, surrendered after being shot in the leg by a police officer in a store, emerged wearing only his underwear and repeatedly asked officers to call his mother. His lawyers do not dispute that he was the shooter.

However, his reasons for committing the mass shooting remain unknown as his trial is set to begin this week.

The closest testimony to a possible motive that has emerged so far comes from a mental health expert who testified during a competency hearing last year that Alissa said he bought the firearm to carry out a mass shooting and suggested he wanted police to kill him.

Robert Olds, whose niece, Rikki Olds, 25, was Alissa’s manager when she was fatally shot at close range as she entered, plans to sit in his usual front-row seat throughout the trial. While he sometimes wishes Alissa had simply been killed, he hopes he will one day learn why his niece, known for her sense of humor and outgoing personality, and others were killed. He is becoming less hopeful, but he is certain that Alissa knew what she was doing.

“I hope he spends the rest of his life in prison and then meets God and answers for killing 10 people, when he will suffer real punishment,” he said.

The trial is expected to focus largely on Alissa’s mental state at the time of the shooting. He has been diagnosed with schizophrenia and has pleaded not guilty by reason of insanity, and his lawyers argue he should be acquitted because his mental illness prevented him from knowing right from wrong.

The defense argued in court papers that his relatives said he irrationally believed he was being followed by the FBI and was talking to himself as if he was talking to someone who wasn’t there. But prosecutors point out that Alissa had never been treated for mental illness before and was able to work up to 60 hours a week before the shooting, something they say would not be possible for someone with severe mental illness.

Alissa faces 10 counts of first-degree murder, 15 counts of attempted murder and other offenses, including being prohibited from possessing six high-capacity magazines in Colorado after earlier mass shootings.

Alissa’s trial was delayed after experts repeatedly found he was unable to understand the legal proceedings or assist in his defense. But after Alissa improved after being forcibly medicated, Judge Ingrid Bakke ruled in October that he was mentally competent, allowing the case to resume.

Prosecutors will have to prove he was sane, trying to show that Alissa knew what he was doing and intended to kill people in the store.

The defense said authorities did not explain why Alissa bypassed a King Soopers store near his home in the Denver suburb of Arvada and drove about 15 miles (24 kilometers) to a store in Boulder, a city she had never been to before the shooting.

Prosecutors presented evidence that Alissa had researched things like how to move and fire an assault rifle and what types of bullets were most deadly in the months leading up to the shooting. One court document noted without explanation that he was researching “the Christ Church attacks,” an apparent reference to the live-streamed shooting attacks by a white nationalist on two mosques in Christchurch, New Zealand, that killed 51 people in March 2019.

Alissa emigrated from Syria with his family as a young child. He lived with his family in Arvada, where they ran a restaurant.

Alissa’s only known problem before the shooting was a 2018 incident in high school when he was convicted of assaulting a classmate, according to police documents. A former classmate also told The Associated Press that Alissa was kicked off the wrestling team after he yelled he would kill everyone after losing a practice match.

According to court documents, Alissa’s sister-in-law, who lives at the home, told police that two days before the shooting, her husband had been playing with what she believed to be a “machine gun” before two relatives took it away from him.

Several of Alissa’s relatives are listed as potential defense witnesses during the trial. Potential jurors will begin questioning Tuesday, and opening statements are expected before the end of the week.

Both sides will rely on expert testimony about his sanity, possibly including tapes of their interviews with Alissa, said defense attorney Karen Steinhauser, a former prosecutor and law professor at the University of Denver.

If the jury does not believe Alissa was found legally insane, they could also consider whether his mental illness prevented him from acting thoughtfully and purposefully, and then find him guilty of second-degree murder, she said.

A sanity evaluation by experts at a state mental hospital found that Alissa was legally sane at the time of the attack, according to details provided by the defense at a court hearing this spring. The defense said evaluators said the attack would not have happened if not for Alissa’s untreated mental illness, which defense attorney Sam Dunn described as schizophrenia that includes “auditory hallucinations.”

Olds said he was preparing to learn more horrifying details about the shooting, including surveillance footage that had not been previously released to the public.

But he added that the fact that the trial is now behind him will help him and many families finally grieve what they have lost.

“There is no such thing as moving on. It is finding other ways to live without your loved one,” he said.