(CNN) — A 25-year-old bank employee opened fire at his workplace in downtown Louisville, Kentucky, Monday morning and livestreamed the attack that left five dead and eight others injured, authorities said.

The gunman was identified as Connor Sturgeon, an employee at Old National Bank, according to interim Louisville Metro Police Chief Jacquelyn Gwinn-Villaroel. He was killed by police after a shootout with authorities.

Four of the victims, who died Monday morning, were identified as Joshua Barrick, 40; Juliana Farmer, 45; Tommy Elliott, 63; and James Tutt, 64, the chief said. Later that evening, police said a fifth victim — 57-year-old Deana Eckert — also died.

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Authorities initially said nine others were injured in the attack, including a 26-year-old police officer who graduated from the police academy just 10 days ago and was shot in the head. Five of those injured had gunshot wounds, a hospital spokesperson said. Later Monday night, police said Eckert, one of the injured victims, had passed away, bringing the death toll to five.

The mass shooting began at the Old National Bank on East Main Street just after 8:30 a.m. police said, about 30 minutes before the bank opens to the public. It happened during a morning employee meeting, with some appearing in person and others virtually, Rebecca Buchheit-Sims, a manager at the bank, told CNN. She watched from her computer as her coworkers were gunned down.

Officers got to the bank within three minutes of being dispatched and found the shooter was still firing, Louisville Metro Police Deputy Chief Paul Humphrey said. Officers got into a shootout with the gunman, killing him, Gwinn-Villaroel said.

Mayor Craig Greenberg thanked the “brave and heroic” first responders for their actions. “Without a doubt their actions saved lives,” he said.

In the aftermath of the shooting, a large police presence blocked off much of the downtown street. Shattered glass was strewn at the entrance of the Old National Bank, video from CNN affiliate WDRB shows.

The shooting is just the latest spasm of mass gun violence, a uniquely American phenomenon. There have been at least 145 mass shootings in the US this year, according to data from the Gun Violence Archive, which like CNN, defines a mass shooting as one in which at least four people are shot, excluding the shooter.

The gun used in the shooting was an AR-15-style rifle, a federal law enforcement source told CNN. The AR-15, a semi-automatic rifle, is the most popular sporting rifle in the US, and about 24.6 million people have owned an AR-15 or similarly style rifle, according to the 2021 National Firearms Survey.

The AR-15 and its offshoots have been the weapon of choice in many of the most heinous mass shootings in recent memory, including in the Sandy Hook school in Connecticut; an Aurora, Colorado, theater; a San Bernardino, California, holiday party; and a Buffalo, New York, supermarket. In Nashville, just two weeks ago, a shooter used an AR-15 style weapon and two other guns in a mass shooting at a private Christian elementary school, killing three adults and three 9-year-olds.

Gunman was notified he was going to be fired, source says

Sturgeon had worked at the bank for more than a year but had been notified he was going to be terminated, according to a law enforcement source familiar with the investigation.

Sturgeon wrote a note to his parents and a friend indicating that he was going to open fire in the bank, the source said. It is not clear whether that note was on paper or emailed, or whether it was seen before the incident or after, according to the source.

The shooting was livestreamed on Instagram and has been taken down but not immediately after the shooting. Police are in possession of the video, according to the source.

Sturgeon wrote on his LinkedIn profile that he interned at the bank for three consecutive summers between 2018 and 2020 before joining full time in June 2021.

He graduated from the University of Alabama in December 2020 with a bachelors and masters degree in finance, according to a spokesperson for the university.

A former high school classmate who knew him and his family well said he never saw any “sort of red flag or signal that this could ever happen.”

“He was a really good kid who came from a really good family,” said the classmate, who asked not to be identified and has not spoken with Sturgeon in recent years. “I can’t even say how much this doesn’t make sense. I can’t believe it.”

In a 2018 college essay posted to the website CourseHero, a user identified as a University of Alabama student named Connor Sturgeon wrote that he had had trouble fitting in at school.

“My self-esteem has long been a problem for me,” the essay read. “As a late bloomer in middle and high school, I struggled to a certain extent to fit in, and this has given me a somewhat negative self-image that persists today. Making friends has never been especially easy, so I have more experience than most in operating alone.”

The author wrote that in college, he had “begun to mature socially and am beginning to see improvement in this area,” and that he hoped to “be more self-aware and start becoming a ‘better’ person.”

Rookie officer was shot in the head, police say

Nickolas Wilt, a 26-year-old rookie officer, ran toward the gunfire and was shot in the head, the police chief said. He is in critical condition.

Wilt had graduated from the police academy on March 31, just 10 days before the shooting.

At a news conference Monday, Gov. Andy Beshear said one of those killed in the shooting, Tommy Elliot, was “one of my closest friends.” Elliott was a senior vice president at the bank, according to his LinkedIn.

“Tommy Elliott helped me build my law career, helped me become governor, gave me advice on being a good dad,” Beshear said. “He’s one of the people I talked to most in the world and very rarely were we talking about my job. He was an incredible friend.”

‘I witnessed people being murdered.’ witness says

Buchheit-Sims said the shooting unfolded very quickly as she watched the bank’s morning meeting virtually.

“Shortly after the meeting started, the gunman, which is an employee, started shooting up the conference room,” Buchheit-Sims said. “I witnessed people being murdered. I don’t know how else to say that.”

Caleb Goodlett got a call from his wife, who works at Old National Bank, he told CNN affiiliate WLKY. She told him there was an active shooter and she was locked in a vault inside the bank. Goodlett called 911 but officers were already aware of the shooting.

He described it as a traumatic phone call at 8:30 a.m., and said he has since talked to and seen his wife and that she is fine.

Hagan Curd was walking his dog on East Main Street on Monday morning when he began to see people running in his direction, he said. Several gunshots can be heard in video he took at the scene.

“I saw people running and then some others got out (of) their car and began to run as well,” Curd said. “Then I heard police yelling and telling people there was a shooter at the bank and to back away.”

The Old National Bank is dual-headquartered in Evansville, Indiana, and Chicago and has more than 250 banking centers across the Midwest. The bank’s executive team is headed to Louisville, the company said on Facebook.

“The safety of Old National Bank employees and everyone we serve in our banking center locations is paramount,” said Old National CEO Jim Ryan. “As we await more details, we are deploying employee assistance support and keeping everyone affected by this tragedy in our thoughts and prayers.”

The Louisville metro area, located along Kentucky’s border with Indiana, has a population of about 630,000 people as of the 2020 Census. The 300 block of East Main Street is bordered to the east by the minor league stadium Louisville Slugger Field and includes a dentist’s office, a furniture store and the Louisville Ballet.

President Joe Biden condemned the latest mass shooting and called on Republicans in Congress to take action on gun laws.

“Once again, our nation mourns after a senseless act of gun violence — Jill and I pray for the lives lost and impacted by today’s shooting. Too many Americans are paying for the price of inaction with their lives. When will Republicans in Congress act to protect our communities?” Biden said in a tweet.

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