A Minneapolis police officer drew her gun by mistake, instead of her Taser, when she fatally shot a young black man during a traffic stop, a police chief says, hours before a second night of unrest sparked by the killing.
Family members of the slain motorist, Daunte Wright, 20, rejected the notion that a mere accident was to blame for Sunday's shooting in Brooklyn Center, Minnesota, with Wright's grieving brother denouncing the police as "trigger happy."
The shooting roiled a region already on edge, as last year's killing of George Floyd, a black man who died with his neck pinned to a Minneapolis street under a white policeman's knee, was being recounted in graphic detail in the trial of former officer Derek Chauvin, charged with his murder.
Wright was killed just 16km from where Floyd, 46, lost his life while under arrest for allegedly passing a bogus $US20 bill, unleashing a months-long nationwide upheaval of protests against racial injustice in the US law enforcement system.
Brooklyn Center's police chief, Tim Gannon, said during a news briefing on Monday that Wright was pulled over for an expired vehicle registration and that the shooting was apparently unintentional, judging from his initial review of police video footage of the incident.
"This appears to me, from what I viewed and the officers' reaction and distress immediately after, that this was an accidental discharge that resulted in the tragic death of Mr Wright," said Gannon.
The Hennepin County medical examiner on Monday ruled the death a homicide, confirming in an autopsy that Wright was killed by a gunshot wound to the chest.
Sunday's shooting immediately ignited a night of street skirmishes between police and protesters in Brooklyn Center, with local news media reporting looting and burglaries of about 20 businesses at a nearby shopping centre.
Disturbances flared anew on Monday, as hundreds of protesters braving a steady downpour and defying a curfew ordered by Governor Tim Walz clashed with law enforcement as darkness fell outside police headquarters in Brooklyn Center.
A crowd surged against a fence erected to keep protesters at bay, some hurling bottles and other projectiles and lighting off fireworks as police responded by firing volleys of tear gas and what appeared to be non-lethal plastic rounds.
A nearby discount store was looted and vandalised, but most of the demonstrators drifted away by 10pm local time. As calm was restored, police reported 40 arrests in Brooklyn Center for offences ranging from curfew violations to rioting charges.
Three officers suffered minor injuries from debris thrown at them, authorities said.
During a memorial vigil on Monday evening at the spot where Wright was killed, relatives remembered him as a good-natured father who worked multiple jobs to support his 2-year-old son.
"My brother lost his life because they were trigger happy," his older half sibling, Dallas Wright, told the crowd.
"My heart is broken in a thousand pieces... I miss him so much, and it's only been a day," his mother, Katie Wright, said as she wept.
"He was my life, he was my son and I can never get that back. Because of a mistake? Because of an accident?"
Police video footage showed one officer trying to handcuff Wright next to the car, before Wright broke free and got back into his car. At that point, a second officer yells, "Taser, Taser, Taser," before firing a single shot from her handgun, the video shows.
"Holy shit, I just shot him," the policewoman is heard to shout.
The police officer who fired the fatal shot, later identified as 26-year department veteran Kim Potter, who is white, was placed on administrative leave. Mayor Mike Elliott called for her immediate dismissal.