Alissa 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 supermarket, according to an arrest affidavit.

While most Colorado court proceedings have been conducted with suspects appearing by video during the pandemic, District Judge Thomas Francis Mulvahill ordered Alissa to appear before him in court though the public and the media were not allowed inside.

Dozens of media trucks and reporters stood outside the courthouse on a cold, clear Colorado morning. There was no sign of protesters or victims’ families.

In addition to Boulder police 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.

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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 US as a toddler and later became a US citizen. He would need to be a citizen to buy a gun. The officials were not authorised to speak publicly and spoke 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 authorised to speak publicly and spoke on condition of anonymity.

More than 500 people bundled in winter jackets and wool hats attended a downtown candlelight vigil on 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.

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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.”

Earlier on 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 on Monday could retrieve them.