Dramatic video has emerged showing hero police officers shooting and killing the Dayton gunman as he sprayed bullets into a crowd of terrified victims.
Masked Connor Betts' rampage lasted less than a minute but he managed to fatally shoot nine people, including his younger sister Megan using a modified .223-calibre automatic rifle.
In the video, screaming revellers crouch down and run for their lives along a pavement as 24-year-old Betts, wearing body armour and black clothing, fires dozens of shots from a gun equipped with a “double-drum” magazine that could hold 100 rounds.
As the crowd clears, Betts appears in the camera's view and is gunned down by police outside the doors of Ned Peppers Bar, stopping America's second gun massacre in just 13 hours.
Betts drops to the floor and tries to get back onto his feet.
A different camera shows officers, armed with their service weapons, running towards the active shooter and taking him out with a volley of shots.
Witness Anthony Reynolds told Reuters he heard gunfire that sounded like it was coming from a high-powered weapon.
He added: "Just boom, boom, boom, rapid.
"You could tell there's a big gun. You're not going to get those from no handgun. You're not."
The CCTV video was released by police after Betts killed nine and wounded at least 27 others.
The nine victims were five men and four women ranging in age from 22 to 57. Six were African-American.
Betts' 22-year-old sister Megan, the youngest of the nine victims, was among the first to be killed.
Betts had arrived with her earlier in the evening, but they separated before the rampage, according to police.
The neighbourhood in Dayton, Ohio, was crowded when Betts launched the attack at about 1am on Sunday.
Officers were on patrol nearby and arrived at the scene in less than a minute.
Betts was shot dead moments after he opened fire, as the officers likely preventing a much higher death toll.
Police Chief Richard Biehl said: "Officers acted ... instantaneously and effectively ended this in 30 seconds."
He added: "Had this individual made it through the doorway of Ned Peppers with that level of weaponry, there would have been catastrophic injuries and a loss of life."
The motive behind the shooting was not immediately clear.
Betts, a white male from nearby Bellbrook, Ohio, was armed with an AR-15-style rifle fitted with an extended drum magazine that could hold 100 rounds.
He was also wearing ear protection and had a shotgun in his car, police said.
The rifle was bought legally online from a dealer in Texas and shipped to a local gun dealer, and it had been modified since it was sold.
Betts had a record for relatively minor traffic offences, but they did not preclude him from purchasing such a weapon.
Sunday's shooting in Dayton came just 13 hours after a mass shooting at a Walmart store in El Paso, Texas, where 20 people were killed and 26 others wounded.
That massacre is being treated as a case of domestic terrorism.
Prosecutors will seek the death penalty for the 21-year-old suspect, Patrick Crusius.
The El Paso shooting happened a week after 19-year-old Santino William Legan killed three people with an assault rifle at a food festival in Gilroy, California before taking his own life.
