BOULDER, Colo. (NewsNation Now) — A 21-year-old suspect in the mass shooting at a Colorado supermarket that left 10 people dead appeared in court for the first time Thursday.

The lawyer for Ahmad Al Aliwi Alissa asked the judge for a mental health assessment. Defense attorney Kathryn Herold provided no other details about what he might suffer from.

During the brief hearing, Alissa appeared in court wearing a mask. He didn’t speak other than to say yes to a question from the judge and did not enter a plea to the charges.

Alissa, 21, remains held without bail on 10 charges of first-degree murder, and a prosecutor said that authorities planned to file more charges.

A law enforcement official briefed on the shooting had previously said the suspect’s family told investigators they believed Alissa was suffering some type of mental illness, including delusions.

Relatives have described times when Alissa told them people were following or chasing him, which they said may have contributed to the violence, the official said. The official was not authorized to speak publicly and spoke to The Associated Press on condition of anonymity.

The attack happened Monday after Alissa arrived at the King Soopers store in Boulder armed with an AR-style semi-automatic rifle and a handgun and wearing a tactical vest, according to the affidavit.

The affidavit also said law enforcement databases show that six days earlier Alissa purchased a Ruger AR-556 pistol, a weapon that resembles a semi-automatic rifle with a slightly shorter stock. Authorities have not disclosed where the gun was purchased.

The massacre was the country’s second mass shooting in a week, after another gunman shot eight people to death at three Atlanta-area spa businesses on March 16.

The twin attacks prompted President Joe Biden to call on Congress to strengthen gun restrictions. Legislation to bolster background checks and ban certain semi-automatic rifles has stalled amid Republican opposition.

Investigators have not yet established a motive, according to Boulder County District Attorney Michael Dougherty.

The law enforcement official who was briefed on the shooting said the suspect’s family told investigators that Alissa had delusions and that they believed he was suffering some type of mental illness. The relatives described times when Alissa told them people were following or chasing him, which they said may have contributed to the violence, the official said.

Alissa, a naturalized U.S. citizen from Syria who graduated from Arvada West High School in 2018, pleaded guilty to third-degree assault for punching a classmate in late 2017.

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

Alissa was sentenced to probation and community service.

The 10 victims on Monday 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.

Witnesses told police the assailant killed one man in his vehicle and then gunned down another in the parking lot. The shooter stood over him, firing multiple times, before entering the store to continue the rampage.

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

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

Colorado has seen some of the most shocking episodes of gun violence in U.S. history, including the 2012 mass shooting at a movie theater in Aurora and the 1999 rampage at Columbine High School, near Littleton. 

Monday’s attack was the seventh mass killing this year in the U.S., according to a database compiled by the AP, USA Today and Northeastern University.

The Associated Press and Reuters contributed to this report. Reporting by Reuters’ Dan Whitcomb and AP’s Patty Nieberg, Thomas Peipert and Colleen Slevin.