A man opened fire at a mall in the US state of Indiana on Sunday, killing three people and wounding two, officials said.
No motive has been established. The incident is the latest armed rampage in a country plagued by gun violence.
The attack ended when a “good Samaritan” shot the gunman dead, AFP quoted the police as saying.
“We experienced a mass shooting this evening at the Greenwood Park Mall,” said Greenwood mayor Mark Myers.
The town is about 16 kilometres to the south of the city centre of state capital Indianapolis.
The gunman, who has not been identified, entered the mall's food court at about 6pm local time, carrying a rifle along with several magazines of ammunition and opened fire, Greenwood Police Department chief Jim Ison said.
Those wounded included a girl, 12.
“Four have been confirmed deceased,” he said, noting that the number included the gunman.
Chief Ison praised the intervention of the armed passer-by, 22, who ended the attack, calling him a “good Samaritan”.
“The real hero of the day is the citizen that was lawfully carrying a firearm in that food court and was able to stop this shooter almost as soon as he began,” he said.
“This has shaken us to our core. This isn't something we have seen in Greenwood before. It's absolutely horrendous.”
It is the latest attack in a wave of gun violence plaguing the US, where about 40,000 deaths a year are caused by firearms, according to the Gun Violence Archive.
The attack comes weeks after a gunman opened fire on a July 4 parade in an affluent Chicago suburb, killing seven people and wounding at least three dozen.
The recent surge in gun violence has reignited the divisive debate over firearm regulation.
A US House of Representatives' committee is set this week to discuss a bill that would ban assault weapons for the first time in about 20 years.
A 10-year federal assault weapons ban expired in 2004.