BALTIMORE (AFP) - The manslaughter trial of a US policeman accused over the death in custody of African-American Freddie Gray was declared a mistrial on Wednesday (Dec 16) after the jury failed to a reach a verdict.

William Porter was the first of six police officers to stand trial for the death of the 25-year-old Gray, who suffered a snapped spine while being transported unrestrained in the rear of a Baltimore police van in April.

Gray's death sparked protests and riots in the East Coast city and was just the latest of several high-profile cases casting a harsh national spotlight on race and police brutality in the United States, particularly in law enforcement relations with black men and youths.

Judge Barry Williams declared a mistrial after the jury of five men and seven women was hung following two days of deliberations.

Porter, who is black, had been charged with involuntary manslaughter, reckless endangerment and assault on Gray, who had been picked up after fleeing at the sight of the police.

Arrested and charged with possession of a knife, Gray was loaded onto the police van with his hands and feet shackled. When police later checked on their prisoner, he was in a coma with a severed spine, investigators found.

He died of his injuries on April 19, sparking protests, looting and arson.

The Baltimore city prosecutor filed charges against six officers - three white and three black - in connection with his death. All six have entered not guilty pleas.

Lawyers for the accused call Gray's death a tragic accident possibly caused when the police van braked suddenly. They also have suggested that he might have deliberately injured himself.