The jury is hung in the trial of Officer William Porter, one of six officers indicted in the death of Freddie Gray.
Gray, 25, died of complications due to a severed spine he suffered during a "rough ride" in the back of a police van in April.
Freddie Gray's death sparked civil unrest and rioting that left 20 officers injured and millions of dollars in property damage in Baltimore.
The jury deliberated for three days before informing the judge they were hopelessly deadlocked.
The judge declared a mistrial and a hearing is scheduled for Wednesday to reschedule a trial.
All six officers were indicted in May on misconduct in office and reckless endangerment charges. Porter was the first officer to go on trial.
Porter is free on bail pending a retrial.