A gunman killed three people when he opened fire in an Indiana shopping centre before he was shot dead by a civilian.
Gunshots were heard in the food court of Greenwood Park Mall outside Indianapolis on Sunday night forcing terrified shoppers and staff to run and hide.
Police said the 22-year-old man who took down the shooter was a "hero".
Two other people, including a 12-year-old girl, were injured in the shooting as SWAT teams surrounded the area after a backpack was found in a bathroom.
The lone gunman was armed with a rifle and several magazines of ammunition before a member of the public opened fire and fatally shot him.
Greenwood Police Chief Jim Ison said: "The real hero of the day is the citizen that was lawfully carrying a firearm in that food court and was able to stop the
shooter almost as soon as he began."
The shooting comes amid amid widespread concerns over US gun laws following a number of shootings in schools and workplaces.
A spate of gun massacres since May at a New York grocery store, a Texas elementary school and an Illinois Independence Day parade have renewed fierce US debate over gun regulations.
Indianapolis Assistant Chief of Police Chris Bailey said: "We are sickened by yet another type of incident like this in our country."
