The judge in the murder trial of a white former South Carolina policeman accused of shooting an unarmed black suspect in the back declared a mistrial Monday after the jury said they were deadlocked.

"I so declare this case a mistrial," Judge Clifton Newman told the court. "We're back to square one."

Michael Slager faced murder and voluntary manslaughter charges for shooting and killing motorist Walter Scott after Scott fled a traffic stop and struggled with the officer on April 4, 2015 in North Charleston.

Slager's lawyers argued that Scott's disregard for authority, aberrant behavior and aggressive actions justified the deadly encounter.