A Minneapolis police officer is reportedly set to have his murder charge upgraded while three colleagues will also be charged over the death of African-American man George Floyd.
Derek Chauvin will face a second-degree murder charge for pressing his knee against Mr Floyd's neck, a newspaper reported on Wednesday.
Widely seen bystander video showing Mr Floyd's May 25 death has sparked sometimes violent protests nationwide and around the world.
Mr Chauvin was fired on May 26 and initially charged with third-degree murder and second-degree manslaughter.
The three other officers involved in George Floyd's arrest were also fired but were not immediately charged.
The Star Tribune reported that Minnesota Attorney General Keith Ellison would be upgrading the charge against Chauvin while also charging Thomas Lane, J Kueng and Tou Thao with aiding and abetting second-degree murder.
Lane's lawyer Earl Gray said the report was accurate.
George Floyd's family and protesters have repeatedly called for criminal charges against all four officers as well as more serious charges for Chauvin.
Former Minneapolis police officer Derek Chauvin has been charged with second-degree murder. Source: AAP
The officer held his knee to Mr Floyd's neck, despite his protests that he couldn't breathe, and stayed there even after he stopped moving.
Mr Floyd was in handcuffs when he died with his face pressed to the street.
Records show Chauvin served as a military policeman in the US Army in the late 1990s.
Since being hired as a police officer in 2001, he has been awarded two medals of valour.
Demonstrators protest the death of George Floyd, near the White House in Washington. Source: AP
Chauvin was reprimanded in 2008 for pulling a woman out of her car in 2007, frisking her and placing her in his squad car after he stopped her for speeding.
His dashboard camera was not activated and a report said he could have interviewed the woman while standing outside her car.
Governor Tim Walz and the Minnesota Department of Human Rights on Tuesday launched a civil rights investigation of the Minneapolis Police Department and its history of racial discrimination, in hopes of forcing widespread change.
The official autopsy by the county medical examiner concluded that George Floyd's death was caused by cardiac arrest as police restrained him and compressed his neck.
A separate autopsy concluded he died of asphyxiation due to neck and back compression due to Chauvin's knee on his neck and other responding officers' knees in his back, which made it impossible for him to breathe.
