The suspect responsible for the Colorado shooting was already identified by the police as 21-year-old Ahmad Al Aliwi Alissa of Arvada, Colorado.

The Monday's shooting at a King Soopers supermarket in Boulder, Colorado left 10 people dead, including a police officer, who was the first responder at the scene.

Boulder County District Attorney Michael Dougherty said the suspect, whose family emigrated from Syria, had lived most of his life in the U.S., adding that Alissa was undergoing treatment at a hospital and was expected to be jailed into the county jail on late Tuesday, according to a PBS News report.

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'Anti-Social and Paranoid'

In light of the recent event, the suspect's brother described the suspect as very anti-social and paranoid.

"When he was having lunch with my sister in a restaurant, he said, 'People are in the parking lot, they are looking for me.' She went out, and there was no one. We didn't know what was going on in his head," said Alissa's brother as reported by the Independent.

He added that his brother had been outgoing before but turned anti-social when he experienced bullying in high school. 

Alissa's brother also said that his brother's attitude was not a political statement of any kind, adding that it is "mental illness."

According to Jeffco Public Schools spokeswoman Cameron Bell, Alissa reportedly went to the Arvada West High School from 2015 until he graduated in 2018. He attended the wrestling team his junior and senior years.

One teammate from his wrestling team, Dayton Marvel, said that he was "kind of scary" to be around, Denver Post reported. Marvel went on to say that when Alissa lost his match, he quit the team and then yelled in the wrestling room that he was going to kill everybody.

Marvel added that nobody believed him, and all were scared by it and did nothing about it.

"He would talk about him being Muslim and how if anybody tried anything, he would file a hate crime and say they were making it up," Marvel said in a report.

In 2017, Alissa allegedly attacked a classmate. In the case, the affidavit filed that Alissa punched the classmate in the head without warning and continued to punch him despite falling to the ground.

Alissa told officers at the time that they had made fun of him and called him racial slurs weeks earlier.

Colorado Shooting

Boulder police chief, Maris Herold, announced the 10 casualties in the Colorado shooting at a conference on Monday night.

A Boulder police officer was killed and was confirmed as Eric Talley, 51. Talley had been in the force since 2010. At the time, the other victims' names were not released to the public as officers notify their families.

On Tuesday, the police released the other victims' names. They were identified as Neven Stanisic, 23; Rikki Olds, 25; Tralona Bartkowiak, 49; Denny Stong, 20; Suzanne Fountain, 59; Teri Leiker, 51; Kevin Mahoney, 61; Jodi Waters, 65; and Lynn Murray, 62.

Matthew Kirsch, the acting U.S. attorney for Colorado, said "the full weight of federal law enforcement" would support the investigation as agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives joined the Federal Bureau of Investigation in the investigation, The Guardian reported.

President Joe Biden announced Tuesday that flags nationwide would be lowered in memory of the Colorado shooting victims. Alissa has been charged with 10 counts of first-degree murder.

READ MORE: 17-Year-Old Suspect Arrested for Mass Shooting That Killed 5 People, Including Pregnant Woman

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