GEOFF BENNETT: Good evening, and welcome to the "NewsHour."

Yet another American city has joined the seemingly endless list of mass killings at the hands of a gunman.

This time, it's Louisville, Kentucky, where four people were killed today, as well as the shooter.

AMNA NAWAZ: Nine others were injured, including two police officers.

It came two weeks after a school shooting in Nashville, Tennessee, that killed three children and three adults.

Lisa Desjardins begins our coverage.

LISA DESJARDINS: Crime scene tape wraps around the Old National Bank building in Louisville, marking tragedy there and, for a nation on edge, at least the 15th mass killing this year.

Witnesses said the gunman opened fire inside the building, located near Louisville's Slugger Field and Waterfront Park.

Officers arrived within three minutes of dispatch and immediately exchanged gunfire with the shooter.

Interim police Chief Jacquelyn Gwinn-Villaroel: JACQUELYN GWINN-VILLAROEL, Louisville, Kentucky, Metro Police Chief: For my LMPD officers who took it upon themselves to not wait to assess everything, but just went in to stop the threat, so that more lives would not be lost, thank you.

LISA DESJARDINS: Police say the gunman was a 25-year-old man who worked at the bank.

They described his weapon as a rifle.

He left four victims dead on the scene, 63-year-old Tommy Elliot, 64-year-old Jim Tutt, 40-year-old Josh Barrick, 57-year-old Juliana Farmer.

Others were in critical condition, including Nickolas Wilt, a young police officer who was shot in the head.

JACQUELYN GWINN-VILLAROEL: The officer who is in critical condition today, officer Nickolas Wilt, 26 years of age, just graduated from the police academy on March 31.

LISA DESJARDINS: Survivors today grateful to escape a rampage the shooter broadcast on social media.

TROY HASTE, Witness: We have a break room.

And I got in there and shut the door for a second.

And then I was looking around.

I opened the door to see where he was at, and I could see him still shooting.

I didn't see his face.

And then I took off running out the front door.

LISA DESJARDINS: Democratic Governor Andy Beshear spoke as both state leader and a person grieving.

GOV.

ANDY BESHEAR (D-KY): This is awful.

I have a very close friend that didn't make it today and one who's in the hospital that I hope is going to make it through.

Sol, when we talk about praying, I hope people will.

LISA DESJARDINS: Louisville's Mayor Craig Greenberg, also a Democrat, has himself survived gun violence after a shooting in his campaign office last year.

CRAIG GREENBERG, Mayor of Louisville, Kentucky: This was an evil act of targeted violence, and to add to that tragedy, a few blocks away, shortly after this happened, another man lost his life and a woman was shot in completely different act of targeted violence.

The two incidents appear to be entirely unrelated, but they both took lives.

They both leave people scarred, grieving, and angry.

LISA DESJARDINS: As the nation continues a heated debate about gun deaths, Louisville's investigation into today's violence begins, with assistance from the FBI.

For the "PBS NewsHour," I'm Lisa Desjardins.