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 today.

He will be advised at the hearing of the charges he faces and his rights as a defendant. He would 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 on condition of anonymity.

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A green tactical vest and a handgun also were 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 gunfire and someone carrying a gun, 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.

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.

Monday’s shooting occurred despite an attempt by city leaders in Boulder to ban assault weapons. But 10 days before Monday’s rampage, the measure was blocked in court after a lawsuit backed by the National Rifle Association. The ruling was made under a Colorado law that bars local officials from making their own gun laws.

Similar preemption laws have become the norm in over 40 U.S. states since the 1980s. A handful of states still allow local officials to make their own rules on guns. In Florida, officials can be fined up to $5,000 if they do, and in Nevada, they could be subject to hefty damages if laws are struck down in court.

At the federal level, President Joe Biden said Tuesday that “we have to act” to pass legislation and Democrats said they are pushing toward a vote on expanded background checks, but it faces a difficult road in the Senate. Congress has not passed any major gun control laws since the mid-1990s, leaving most significant gun legislation in states’ hands.

Supporters say preemption measures allow states to be consistent in firearm laws so that law-abiding gun owners aren’t facing a patchwork of different rules in different parts of the state. The NRA has called the Boulder ordinance counter-productive, and argued it was a clear violation of Colorado’s preemption law passed in 2003.

Critics, though, argue those measures serve to intimidate any officials considering firearm restrictions.

The ordinance was challenged in court shortly after it passed. The city hasn’t yet decided whether to appeal the ruling.

Information for this article was contributed by Michael Balsamo, Jim Anderson, Lindsay Whitehurst and Michael Biesecker of The Associated Press.

Caution tape marks the parking lot outside a King Soopers grocery store where a mass shooting took place a day earlier in Boulder, Colo., Tuesday, March 23, 2021. (AP Photo/David Zalubowski)

Investigators deal with light snow as they collect evidence in the parking lot where a mass shooting took place in a King Soopers grocery store Tuesday, March 23, 2021, in Boulder, Colo. (AP Photo/David Zalubowski)

Debris lies in the parking lot outside a King Soopers grocery store where a mass shooting took place Tuesday, March 23, 2021, in Boulder, Colo. (AP Photo/David Zalubowski)

Police drive past a makeshift fence put up around the parking lot outside a King Soopers grocery store where a mass shooting took place Tuesday, March 23, 2021, in Boulder, Colo. (AP Photo/David Zalubowski)

Police head into the parking lot outside a King Soopers grocery store where a mass shooting took place Tuesday, March 23, 2021, in Boulder, Colo. (AP Photo/David Zalubowski)

A snow squall envelops investigators as they collect evidence around the parking lot where a mass shooting took place in a King Soopers grocery store Tuesday, March 23, 2021, in Boulder, Colo. (AP Photo/David Zalubowski)

A road closed sign stands along a makeshift fence put up around the parking lot outside a King Soopers grocery store where a mass shooting took place a day earlier in Boulder, Colo., Tuesday, March 23, 2021. (AP Photo/David Zalubowski)

Snow falls as investigators continue to collect evidence in the parking lot where a mass shooting took place at a King Soopers grocery store Tuesday, March 23, 2021, in Boulder, Colo. (AP Photo/David Zalubowski)

A makeshift fence stands around the parking lot outside a King Soopers grocery store where a mass shooting took place a day earlier in Boulder, Colo., Tuesday, March 23, 2021. (AP Photo/David Zalubowski)