A federal investigation has been launched into policing practices in the city of Minneapolis, a day after one of its former officers was convicted of the murder of George Floyd.
The justice department will look at whether there has been a pattern "of unconstitutional or unlawful policing", Attorney General Merrick Garland said.
It follows national outrage over the killing of Mr Floyd by Derek Chauvin.
The former officer was convicted of all charges on Tuesday.
Chauvin was filmed kneeling on Mr Floyd's neck for more than nine minutes during an arrest in May 2020. Mr Floyd, an unarmed African American, was pronounced dead an hour later.
The footage sparked protests across the country, and calls for police reformation.
Tuesday's verdict has been welcomed in a country where police are rarely been convicted - if they are charged at all - for deaths which occur in custody.
But Mr Garland told reporters Tuesday's he knew the verdict would not "address potentially systemic policing issues in Minneapolis".
What will the investigation look at?
The attorney general said the investigation would "include a comprehensive review of the Minneapolis Police Department's policies, training, supervision and use of force investigations".
It will also examine "whether its treatment of those with behavioural health disabilities is unlawful", while looking at the "effectiveness of current systems of accountability and whether other mechanisms are needed to ensure constitutional and lawful policing".
Mr Garland said both the community and law enforcement would have to take part if the investigation were to be a success, and he had already started reaching out to both.
If unlawful patterns or practices were found, he promised to issue a public report and bring a civil lawsuit.
What happened to George Floyd?
The 46-year-old bought a pack of cigarettes at a convenience store in May 2020. A shop assistant believed he had used a counterfeit note and called the police after Mr Floyd refused to give the cigarettes back.
When police arrived, they ordered Mr Floyd out of his parked car and handcuffed him. A struggle ensued when officers tried to put a screaming Mr Floyd in their squad car. They wrestled him to the ground and pinned him under their weight.
Chauvin pressed his knee into the back of Mr Floyd's neck for more than nine minutes.
As he was being restrained, Mr Floyd said more than 20 times that he could not breathe, pleading for his mother and begging "please, please, please".
When the ambulance arrived, Mr Floyd was motionless. He was pronounced dead about an hour later.
How did people react?
A video of the incident prompted outrage around the world, setting off days of demonstrations which spread across the entire US, with reformation of police departments at the heart of protesters' demands.
However, former President Donald Trump largely sided police - although he did sign an executive order asking police departments to improve officers' training and create a database to track misconduct.
His successor Joe Biden has struck a different tone, welcoming the conviction of Chauvin on Tuesday, saying it "can be a giant step forward in the march toward justice in America".