Minneapolis police officers will not be charged over the fatal shooting of Jamar Clark, a 24-year-old unarmed man.
The prosecutor said evidence showed he was not handcuffed when he was shot, contrary to reports at the time.
Police responded in November to an alleged assault by Clark and said he interfered with paramedics.
His death came after a series of fatal US police shootings involving African Americans. Hundreds of people protested in Minneapolis on Wednesday night.
Police said Clark was not handcuffed and tried to seize one of their weapons, and they shot him because they feared he would shoot them.
Witnesses say he was indeed handcuffed and did not struggle with the officers.
One of the officers involved is white and the other one's race has not been released.
The prosecutor, Hennepin County Attorney Mike Freeman, said forensic evidence showed Clark was not handcuffed when he was shot.
Mr Freeman decided earlier not to take the case to a grand jury.
Protesters gathered at a square near government buildings in Minneapolis on Wednesday night, chanting "No justice, no peace, prosecute the police" and singing songs.
Grand juries were used in the fatal shootings of 12-year-old Tamir Rice in Cleveland and 18-year-old Michael Brown in Ferguson, Missouri - two cases which saw no indictments.