BOULDER, Colo. — Law enforcement officials and former associates of a 21-year-old man accused of killing 10 people at a Colorado supermarket have described the suspect as prone to sudden rage — and disclosed that he was suspended from high school several years ago for a sudden attack on a classmate that left the student bloodied.

Ahmad Al Aliwi Alissa, from the Denver suburb of Arvada, was booked into jail Tuesday on murder charges a day after the attack at a King Soopers grocery in Boulder and is scheduled to make his first court appearance Thursday.

He will be advised at the hearing of the charges he faces and his rights as a defendant. He will not be asked to enter a plea until later in the judicial process.

Alissa bought a Ruger AR-556 pistol — which is technically a pistol though it resembles an AR-15 rifle with a slightly shorter stock — on March 16, six days before the attack, according to an arrest affidavit. Investigators have not established a motive, said Boulder County District Attorney Michael Dougherty.

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

A green tactical vest and a hand gun were also recovered inside the grocery store after the suspect removed most of his clothing shortly before he was taken into custody.

Among the dead was Boulder police Officer Eric Talley, 51, who was the first to arrive after responding to a call about shots fired, said police Chief Maris Herold.

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.

After the shooting, detectives went to Alissa’s home and found his sister-in-law, who told them that he had been playing with a weapon she thought looked like a “machine gun” about two days earlier, according to an arrest affidavit.

No one answered the door Tuesday at the Arvada home believed to be owned by the suspect’s father. The two-story house with a three-car garage sits in a relatively new middle- and upper-class neighborhood.

When he was a high school senior in 2018, Alissa was found guilty of assaulting a fellow student in class after knocking him to the floor, climbing on top of him and punching him in the head several times, according to a police affidavit.

Alissa “got up in classroom, walked over to the victim & ‘cold cocked’ him in the head,” the affidavit said.

Alissa complained that the student had made fun of him and called him “racial names” weeks earlier, the affidavit said.

Homer Talley, 74, described his son Eric as a devoted father who “knew the Lord.” He had seven children, ages 7 to 20.

The other dead were identified as 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.