Five people died when an employee opened fire at a bank in Louisville, Kentucky, and livestreamed the attack on Instagram, police say.
The victims were aged between 40 and 64. Among nine others injured was a rookie police officer who had graduated to the force just two weeks ago.
The officer was shot in the head and is still critical after brain surgery.
Police responded within three minutes, and fatally shot the attacker in an exchange of gunfire.
The shooting took place at the Old National Bank in the city centre at about 08:30 local time (12:30 GMT).
Caleb Goodlett told local media that his wife, an employee at the bank, locked herself inside the vault when the attack began.
Other witnesses described seeing the shootout between police officers and the lone attacker.
Kentucky Governor Andy Beshear said an "incredible friend" of his, Tommy Elliot, a senior vice-president at the bank, was among the victims.
"Tommy Elliott helped me build my law career, helped me become governor, gave me advice on being a good dad," said Mr Beshear.
The victims have all been identified:
- Thomas Elliot, 63
- James Tutt, 64
- Joshua Barrick, 40
- Julianna Farmer, 45
- Deana Eckert, 57
The policeman who was shot in the head was identified as Louisville Metro officer Nickolas Wilt, 26.
What we know about the Kentucky bank shooting victims
City Councilman Anthony Piagentini told the Courier-Journal newspaper that Mr Wilt graduated from the academy on 31 March, and that his brother is enrolled in the police academy.
Louisville Mayor Craig Greenberg called the attack "an evil act of targeted violence". The mayor noted that he himself was the victim of a recent gun attack.
Last year he was shot at by a man with mental illness who burst into his campaign office.
Two survivors told WHAS-TV that Monday's gunshots first broke out in a ground-floor conference room at the bank.
"Whoever was next to me got shot - blood is on me from it," said one man, pointing to his shirt.
The suspect was named as 25-year-old Connor Sturgeon, who police said used an AR-15-style semi-automatic rifle during the incident and was broadcasting the shooting online.
"That's tragic to know that that incident was out there and captured," said Police Chief Jacquelyn Gwinn-Villaroel.
Instagram's owner Meta said it had "quickly removed the livestream of this tragic incident this morning".