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.