New charges have been brought against all of the four police officers present at the death of African American George Floyd in Minneapolis on May 25.
The charge against Derek Chauvin has been elevated to second-degree murder, according to court documents.
The other three officers, previously uncharged, now face counts of aiding and abetting murder.
Mr. Floyd’s death has sparked huge protests across the US against racism and the police killings of black Americans.
The vast majority of demonstrations over the past eight days have been peaceful, but some have turned violent and curfews have been imposed in a number of cities.
Announcing the new charges, Minnesota’s Attorney General Keith Ellison said that they were in the interests of justice.
Derek Chauvin, already sacked, had initially faced charges of third-degree murder and second-degree manslaughter.
The other three sacked officers are Thomas Lane, J Alexander Kueng and Tou Thao. They all face charges of aiding and abetting second-degree murder, and aiding and abetting second-degree manslaughter.
A lawyer for the Floyd family, Benjamin Crump, called the new charges “a significant step forward on the road to justice”.”
But he was later to tell CNN that the family believed the charge against Derek Chauvin should be first-degree murder and that they had been told that the investigation was ongoing, and the charges could change further.
At a press briefing, rights activist Rev Al Sharpton said that the Floyd case must lead to a national federal act.
Otherwise, he said, “… all of this is drama to no end”.
Meanwhile, US defence secretary, Mark Esper, has opposed President Trump’s proposal for the use of the military to end the protests and random violence of the last one week.
In an interview on Wednesday, Mr. Esper said soldiers should only be deployed as a last resort.
Analysts say while Mr. Esper’s comments may have invoked the ire of the president, it might yet be difficult for Mr. Trump to fire his defence secretary in such an uncertain election year.