The suspect in the Boulder, Colorado, supermarket mass shooting made his first court appearance on Thursday. 

Ahmad Al Aliwi Alissa, who has been charged with 10 counts of first-degree murder and one charge of attempted murder, appeared in court wearing a mask. He did not speak during the brief hearing, other than to say "yes" to a judge's question, and did not enter a plea in the case.

The 21-year-old suspect has been jailed for investigation of murder since he was arrested inside the King Soopers supermarket in Boulder on Monday and treated at a hospital for a leg wound. He is being held without bail.

His defense attorney, Kathryn Herold, asked for a mental health assessment "to address his mental illness," but did not expand on what he might suffer from.

At Herold’s request, Alissa’s next hearing will not be scheduled for another two to three months to allow the defense team to evaluate his mental health and evidence that is being collected by investigators.

Prosecutors said that they plan to file more charges.

The suspect was last seen handcuffed and being led out of the supermarket by police. He had removed all clothing except his shorts before being taken into custody. A rifle, a green tactical vest and a handgun were recovered inside the grocery store, according to an arrest affidavit.

Relatives have described times when Alissa told them people were following or chasing him, which they said may have contributed to the violence, according to a law enforcement official who spoke to The Associated Press on condition of anonymity.

Hundreds of mourners gathered Wednesday night at a candlelight vigil to remember the 10 people gunned down at a supermarket in a Colorado college town, while the 21-year-old man suspected of carrying out the rampage prepared for his first court appearance Thursday morning.

More than 500 people bundled in winter jackets and wool hats attended a downtown candlelight vigil Wednesday night to mourn the victims and comfort one another. They observed a moment of silence; violins soothed the crowd; a woman sang “Ave Maria” as candle flames flickered in the crisp air. A star-shaped light usually turned on for the holidays glowed on a mountain overlooking the open square.

Michele Weiner-Davis, a Boulder family therapist, offered the community some words of wisdom.

“Whatever you’re feeling, whatever you’re thinking, no matter how uncomfortable, it’s completely natural,” Weiner-Davis said. “Be patient with yourself. Additionally, be just as compassionate with the people in your lives who might also be struggling.”

In addition to Officer Eric Talley, 51, the victims are Denny Stong, 20; Neven Stanisic, 23; Rikki Olds, 25; Tralona Bartkowiak, 49; Suzanne Fountain, 59; Teri Leiker, 51; Kevin Mahoney, 61; Lynn Murray, 62; and Jodi Waters, 65. Leiker, Olds and Stong worked at the supermarket.

Earlier Wednesday, hundreds of people paid their respects during a police procession for Talley as his body was taken to a funeral home in the Denver suburb of Aurora.

Police also announced that people whose cars were left in the supermarket parking lot Monday could retrieve them.

A supermarket employee told the AP she watched as the assailant opened fire and narrowly escaped his notice while joining others in a desperate scramble to get away.

Emily Giffen, 27, was smoking outside the store Monday during a break when she heard multiple loud pops that she knew were not fireworks. She said she saw a man running across an intersection suddenly fall over and another man approach him in a crouch and fire several rounds at close range.

“I don’t know how he didn’t see us,” she said of the suspect, who walked right by her before she ran into the supermarket and out the back.

“I just really am having a hard time understanding why me and my friends deserve to die,” she said, wondering why the gunman chose to target the Boulder store specifically.

According to the arrest affidavit, the suspect bought a Ruger AR-556 pistol — which resembles an AR-15 rifle with a slightly shorter stock — on March 16, six days before the attack. Authorities have not disclosed where the gun was purchased.

According to two law enforcement officials, Alissa was born in Syria in 1999, emigrated to the U.S. as a toddler and later became a U.S. citizen. He would need to be a citizen to buy a gun. The officials were not authorized to speak publicly and spoke to AP on condition of anonymity.

An AR-15-style gun recovered inside the supermarket was believed to have been used in the attack, said a law enforcement official briefed on the shooting who was not authorized to speak publicly and spoke to the AP on condition of anonymity.

The Associated Press contributed to this report.