"We believe this is a lone gunman involved in this, that did have a connection to the bank," Humphrey said. "It appears he was a previous employee." 

    The fast response of officers prevented more deaths and injuries, Louisville police said.

    "It is clear from the officers' response that they absolutely saved peoples' lives," Humphrey said. "This was a tragic event but it was the heroic response of officers that made sure that no more people were more seriously injured than what happened."  

    Mayor Craig Greenberg also thanked officers for their lifesaving actions. Greenberg himself was nearly killed last year when a gunman entered his campaign office, opened fire and grazed his sweater.

    "We come together as a community to work to prevent these horrific acts of gun violence from continuing here and around the state," Greenberg said. "We are a safer community, we are a stronger community thanks to the work of our law enforcement."  

    Police cars, ambulances and firetrucks flooded Main Street between North Floyd and North Preston streets, in the heart of Kentucky’s largest city.

    It wasn't immediately clear if the bank employed a security guard at the location where gunfire erupted Monday.

    "The safety of Old National Bank employees and everyone we serve in our banking center locations is paramount," Old National Bank CEO Jim Ryan said in a statement.

    The bank executive called for "keeping everyone affected by this tragedy in our thoughts and prayers." 

    The incident unfolded in the shadows of Slugger Field, home of the Cincinnati Reds Triple-A affiliate, the Louisville Bats.

    That team was out of town Monday and police used the stadium as a base of operations, appearing to interview witnesses there.

    And as police responded to the Old National Bank, some officers had to peel off for another shooting just a mile away at Jefferson Community and Technical College, officials said.

    The two attacks are not connected and classes at the school were canceled, officials said.

    Senate Minority Leader Mitch McConnell and his wife, Elaine Chao, thanked police for their fast and brave work Monday.

    "Elaine and I are devastated by the news coming out of Louisville this morning," the Kentucky Republican said in a statement. "Thank you to LMPD and our first responders for your bravery at the scene. We send our prayers to the victims, their families, and the city of Louisville as we await more information."

    President Joe Biden issued a statement saying he and first lady Jill Biden were praying for the victims.

    "Once again, our nation mourns after a senseless act of gun violence. ... Too many Americans are paying for the price of inaction with their lives," Biden said. "When will Republicans in Congress act to protect our communities?"

    Monday's gunfire was the latest mass shooting in America and happened just two weeks after six people, including three young children, were gunned down at a private Christian school in Nashville, Tennessee.

There have been several other instances of mass shootings in the workplace just in the past five months: 

    Monday's gunfire also brought back unpleasant memories for longtime Louisville residents who recall Sept. 14, 1989, when disgruntled employee Joseph Wesbecker came to the Standard Gravure printing plant with an AK-47 and killed eight people.

   Wesbecker, 47, died of a self-inflicted gunshot wound at the scene.