Baltimore's top prosecutor says she plans to file criminal charges against six officers in the case of Freddie Gray who died in police custody.
State prosecutor Marilyn Mosby said the death of the 25-year-old black man was a homicide, and his arrest was illegal.
The charges range from second-degree murder to assault. Protesters cheered as she made the announcement.
Gray suffered fatal spinal injuries while in custody, sparking protests that turned violent.
"The findings of our comprehensive, thorough, and independent investigation coupled with the medical examiner's determination was a homicide... has led us to believe that we have probable cause to file criminal charges," Mrs Mosby told a news conference.
Celebrations broke out across Baltimore after the announcement. Drivers honked their car horns as people took to the streets with fists raised in triumph.
She said Mr Gray died as a result of injuries suffered while he was shackled inside a Baltimore police van, but not restrained by a seat belt - as he was legally required to be.
Mayor Stephanie Rawlings Blake said that five of the officers were in custody. The officers were suspended after Gray's death.
"No one in our city is above the law," Ms Blake said. "Justice must apply to all of us equally."
The driver of the van, Caesar Goodson, 45, faces the most serious charge, second-degree murder. Mr Goodson faces more than 30 years in prison if convicted.
The other officers face charges including involuntary manslaughter, assault and misconduct.
"To the people of Baltimore and the demonstrators across America, I heard your call for 'no justice, no peace'. Your peace is sincerely needed, as I work to deliver justice on behalf of this young man." Mrs Mosby said.
Mrs Mosby said that Gray was not carrying a switchblade as reported earlier by police, but a legal pocketknife.
The police union defended the officers and said they acted "diligently". The union called for an independent prosecutor, something Mosby said was not needed.
After Gray's funeral on Monday (local time), riots broke out in sections of West Baltimore. About 200 people were arrested as more than 100 cars were set alight and 15 buildings destroyed.
Since then, the city and state officials deployed thousands of extra law enforcement officers and National Guard troops to keep the peace and enacted a citywide curfew.
Those measures have brought relative calm to Baltimore as thousands have taken part in nightly protests.
President Barack Obama responded to questions about the charges in Washington, saying the legal process should run its course.
"What I think the people of Baltimore want more than anything else is the truth," Mr Obama said.
Ciara Ford of Baltimore expressed surprise at the decision to prosecute.
"I hope this can restore some peace," she told the Associated Press. "If we had kept quiet, I don't think they would have prosecuted."
Gray's death is the latest in a string of high-profile cases where black men have died after contact with the police.