The suspected gunman who shot and killed four people at a downtown Louisville bank had recently been notified he was going to be fired from Old National Bank, law enforcement sources told ABC News.

Connor Sturgeon had interned at Old National Bank for three years before earning a full-time job in June 2021, sources said. He had been promoted in April 2022.

There was no immediate indication why he was notified he would be terminated, according to sources.

The suspect allegedly left a note to parents and friends indicating he was going to shoot up the bank, sources said.

-ABC News' Aaron Katersky

The suspected shooter, 25-year-old Connor Sturgeon, was armed with a rifle when he allegedly carried out a mass shooting at the Old National Bank, where he worked, according to police.

The suspect was livestreaming, police said, though officials did not elaborate.

Authorities said the suspect was killed by police.

Nine people were hospitalized, including three currently in critical condition, said Dr. Jason Smith, chief medical officer at University of Louisville Health. Three victims are in the hospital with non-life-threatening injuries and the three others have been released, Smith said.

Among the nine injured is 26-year-old police officer Nickolas Wilt, who was shot in the head while running toward the gunfire, according to police. He underwent brain surgery and is in critical but stable condition, police said.

Wilt just graduated from the police academy on March 31.

The four slain victims were identified by police as Joshua Barrick, 40; Thomas Elliott, 63; Juliana Farmer, 45; and James Tutt, 64.

Louisville Mayor Craig Greenberg said Elliott was "a very good friend of mine" and of Kentucky Gov. Andy Beshear.

"This was an evil act of targeted violence," the mayor said.

The mayor said that he was also a survivor of a workplace shooting, and said to the survivors, "Whether you were physically hurt or not, I know you’re hurting, too."

"Today, I'm hurt and I'm hurting, and I know so many people out there are, as well," Beshear said. "We lost four children of God today, one whom is one of my closest friends. Tommy Elliott helped me build my law career, helped me become governor, gave me advice on being a good dad. ... He was an incredible friend."

The governor said of all four victims, "These are irreplaceable, amazing individuals."

President Joe Biden tweeted Monday, "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," he wrote. "When will Republicans in Congress act to protect our communities?”

White House press secretary Karine Jean-Pierre said at Monday's briefing, "Once again, today the president has called on Republicans in Congress to work together with Democrats to take action to ban assault weapons and high-capacity magazines, to require safe storage of firearms, to require background checks for all gun sales, to eliminate gun manufacturers' immunity from liability."

"These are common sense actions we can ask for and should be getting right now," she said.

"We need to act and we need Republicans to show some courage," she said.

Two officers and seven civilians were injured in the Louisville shooting, according to the University of Louisville Hospital.

One of those officers is in critical condition, according to police.

At least three patients have already been discharged, according to the hospital.

The alleged gunman in Monday's mass shooting at a Louisville bank was wielding an AR-15 when he was gunned down by police, according to Louisville Mayor Craig Greenberg.

Craig revealed the detail during an interview with CBS News on Tuesday morning.

-ABC News' Victoria Arancio