The suspected gunman in Monday’s horrific shooting in Boulder has been identified as a 21-year-old Ahmad Alyssa.

Police say he entered the King Soopers supermarket and opened fire in the afternoon, killing 10.

He exchanged gunfire with cops before he was taken into custody.

Ahmad Al Aliwi Alissa, 21, of Arvada, Colo., now faces 10 counts of first-degree murder for the rifle rampage he unleashed Monday afternoon in a King Soopers grocery store in Boulder, Colo., where some shoppers were out getting COVID-19 vaccines, officials said at a Tuesday briefing.

“We will hold the evildoer responsible to the full extent of the law for his actions,” said Democratic Gov. Jared Polis. “And we will always remember the victims of the King Soopers shooting.”

Alissa’s now-deleted Facebook page said he was “born in Syria in 1999 came to the USA in 2002,” the Daily Beast reported.

He included postings about Islam, such as its prayers and religious holidays, on his account — and shared another person’s thoughts the day after the mosque massacres in Christchurch, New Zealand, that killed 51 people in 2019.

“The Muslims at the #christchurch mosque were not the victims of a single shooter,” rea the post on Alissa’s page, according to the Daily Beast. “They were the victims of the entire Islamophobia industry that vilified them.”

The suspect, who was shot in the leg and is hospitalized in stable condition, is expected to be transferred to a local jail later Tuesday, at which point an arrest affidavit and warrant will be made public, authorities said.

Authorities have already interviewed Alissa, but they did not disclose Tuesday what, if anything, he said about his motive.

“Why did this happen?” asked Boulder County District Attorney Michael Dougherty at the briefing. “We don’t have the answer to that yet, and the investigation is in its very early stages.”

But the alleged shooter’s older brother told the Daily Beast that he believes his sibling is mentally ill.

“When he was having lunch with my sister in a restaurant, he said, ‘People are in the parking lot, they are looking for me,’” Ali Aliwi Alissa, 34, told the outlet. “She went out, and there was no one. We didn’t know what was going on in his head.”

He described his brother as “very anti-social,” and said that when the alleged gunman was in high school, he would describe “being chased, someone is behind him, someone is looking for him.”

At the briefing, authorities said that Alissa appears to be the only suspect, and that he had no prior run-ins with local police.

But local Fox affiliate KDVR obtained court documents from 2017 showing that Alissa was busted for “cold cocking” a classmate at school.

The victim was left with bruising, swelling and cuts to the head from the assault, the outlet reported.

Alissa apparently snapped because the victim “had made fun of him and called him racial names weeks earlier,” according to the documents, which indicate Alissa pleaded guilty to assault in 2018.

Alissa’s brother told The Daily Beast that, in addition to being mentally ill, his sibling had been bullied throughout high school.

“[It was] not at all a political statement, it’s mental illness,” Ali Aliwi Alissa said of the mass shooting. “The guy used to get bullied a lot in high school, he was like an outgoing kid but after he went to high school and got bullied a lot, he started becoming anti-social.”

A high school wrestling teammate of Alissa’s recalled his fiery temper.

“One thing I can tell you is he didn’t take losing very well,” the teammate, identified only as Conrad, told The Daily Beast. “He would throw his headgear, wouldn’t talk to the coaches when he lost. If I remember correctly, even cussed out one of the coaches one time.”

Still, Conrad told the outlet that he was surprised by the allegations.

The 10 victims were also identified at the press conference — including slain Boulder police officer Eric Talley.

They range in age from 20 to 65, according to Boulder Police Chief Maris Harold, who said the last body was removed from the scene at 1:30 a.m. Tuesday.

Family members were notified about two hours later.

“I want to say to the community, I am so sorry this incident happened,” the chief said with tears in her eyes. “We are going to do everything in our power to make sure this suspect has a thorough trial and we do a thorough investigation.”

Doughtery said Talley, who was the first officer on scene, “died heroically.”

“He died charging into the line of fire to save people who were simply trying to live their lives and go food shopping,” he said. “And the man who gunned them down will be held fully responsible.

“The killer, his name will live in infamy,” said Dougherty. “But today, let us remember the victims.”

Meanwhile, US Rep. Joe Neguse, who represents Colorado’s Second District encompassing Boulder, decried other recent shootings in the state.

“This cannot be our new normal,” he said. “We should be able to feel safe in our grocery stores. We should be able to feel safe in our schools, in our movie theaters and in our communities. We need to see a change.”