Ahmad Al Aliwi Alissa, charged with gunning down 10 people at a supermarket in the US state of Colorado college town, has been ordered by a court to be held without bail.

Alissa made his first court appearance on Thursday since the killings. His lawyer, Katherine Herold, asked for a mental health assessment “to address his mental illness”, without offering details on what that illness is.

During the brief hearing, Alissa appeared in court wearing a mask. He did not speak anything, except “yes” in reply to a question from the judge, and did not enter a plea to the charges.

Alissa faces 10 counts of murder and an attempted murder stemming from the shooting rampage on Monday at King Soopers grocery store in Boulder, Colorado. The 21-year-old was arrested from the supermarket.

According to the arrest affidavit, Ahmad Alissa bought a Ruger AR-556 pistol – which resembles an AR-15 rifle with a slightly shorter stock six days before the attack [Boulder Police Department/Handout via Reuters]
He was last seen handcuffed and being led out of the supermarket by police on Monday. He had removed all clothing except his shorts before being taken into custody. He was bleeding from his leg. Colorado officials described the wound as a shot that went through his leg. He was hospitalised before being taken to jail on Tuesday.

A rifle, a green tactical vest and a handgun were recovered from the grocery store, according to an arrest affidavit.

Alissa was born in Syria in 1999. He emigrated to the US when he was three, and later became a US citizen.

According to the affidavit, he 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 bought.

When apprehended, Alissa did not answer questions but asked to speak with his mother, according to the affidavit.

Police have not yet publicly identified a motive for the killings. Alissa’s 34-year-old brother described him as antisocial and paranoid in an interview with the Daily Beast.

People laying flowers on the police car of officer Eric Talley who died on Monday responding to a shooting call [Kevin Mohatt/Reuters]
The suspect’s sister-in-law told police on Monday evening that he had been “playing with” a firearm she described as resembling a “machinegun” two days earlier, upsetting family members, according to the arrest affidavit filed by the police in the case.

In late 2017, Alissa pleaded guilty to third-degree assault for punching a classmate.

The classmate said the attack was unprovoked, an account supported by interviews with several witnesses, according to an Arvada Police Department incident report at the time. Alissa told an officer the classmate had called him a “terrorist” and racist names.

Alissa was sentenced to probation and community service.

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.

Mourners gathering at a candlelight vigil at Cornerstone Boulder church to pray for the victims of the shooting [Alyson McClaran/Reuters]
The shooting victims included Eric Talley, an 11-year veteran of the Boulder police force who was among the first officers on the scene. Talley, 51, was a father of seven who had been looking for less dangerous work, according to his father.

Also killed were 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 Jody Waters, 65. Stong, Olds and Leiker worked at the store.

Makeshift memorials of flowers, votive candles and condolence messages were left this week outside the supermarket and at the police headquarters.