Baltimore Police Commissioner Anthony Batts told reporters that a team of investigators had carried out an urgent examination of events surrounding the April 12 arrest of Freddie Gray and his death a week later.
"I understand the frustration, I understand the sense of urgency, and so has the organization and that is why we have finished (the probe) a day ahead of time," Batts said.
"The state's attorney is committed to seeing justice. And from this point on, we will take all directions from the state attorney, because it is now their case."
Gray, 25, died of spinal injuries apparently suffered during his arrest or soon after. His death sparked riots in Baltimore and protests in cities on the US East Coast, including New York, Washington and Boston.
Gray died with 80 percent of his spine severed at the neck, lawyers for his family say, portraying him as just the latest young African American to die at the hands of the police.
In August, a white policeman shot dead a black teenager in the St Louis suburb of Ferguson, triggering demonstrations in major US cities from Los Angeles to New York that were repeated when a grand jury declined to indict the officer.
