As a march processed through the street in the state’s capital city on 25 July, a car turned right into the crowd as it accelerated through a red light at an intersection, video shows.
The crowd surrounded the car, and a man then extended an arm through the driver side window and fired several shots, police said.
Garrett Foster, a 28-year-old racial justice supporter and US Air Force veteran, who also was a Second Amendment proponent and carried a rifle with him during the protest, was hit and rushed to a nearby hospital, where he was pronounced dead.
A suspect has been arrested and is cooperating with officers, according to Katrina Ratcliff with the Austin Police Department’s public information office.
Eight gunshots can be heard in a video of the demonstration, followed by screams from protesters running from the scene as the car sped away.
Mr Foster brought an AK-47 rifle to the demonstration, which is legal in the state if the guns are not used to threaten or harm others. Police believe two people fired weapons, though police clarified Mr Foster did not fire his rifle.
“They don’t let us march in the streets anymore, so I got to practise some of our rights,” Mr Foster told journalist Hiram Gilberto Garcia, who was filming the protest on Periscope, earlier that night.
Witnesses said that Mr Foster was pushing his fiancee in her wheelchair alongside the demonstration. She was not injured in the shooting.
Mr Foster, who is white, and his fiancee Whitney Mitchell, who is black, participated in several demonstration against police brutality in the Austin area following the killing of George Floyd in Minneapolis, according to witnesses.
A memorial fund in Mr Foster’s name had raised more than $65,000 as of 26 July.
Mr Foster’s death marked yet another violent night amid nationwide demonstrations against the killing of black Americans.
In Portland, police declared Saturday’s protest a riot after a group compromised fencing around a federal court building where federal officers deployed in the city have staged.
Seattle protests also were declared a riot by police after a fire was set near a juvenile detention centre. Federal officers also have been deployed in that city, despite calls from local officials to withdraw.