A North Carolina judge declared a mistrial Friday after a jury deadlocked in the case of a white police officer charged with voluntary manslaughter in the death of an unarmed black man.

Judge Robert C. Ervin in Charlotte declared a mistrial Friday afternoon after four days of deliberations.

Ervin brought the racially diverse jury back into the Mecklenburg County courtroom around 4:10 p.m. and the foreman said he saw no possibility of reaching a verdict.

"Honestly, we have exhausted every possibility," the foreman said.

Charlotte-Mecklenburg Police officer Randall Kerrick had faced up to 11 years in prison.

The jury had deliberated for four days.

Prosecutors said the 29-year-old Kerrick used deadly force when he shot and killed Jonathan Ferrell in September 2013. They say nonlethal force should have been used to subdue the former Florida A&M football player. Two officers with Kerrick didn't fire their guns.

But Kerrick's attorneys said the officer feared for his life when he shot and killed Ferrell while responding to a breaking-and-entering call.

The case was one of several in recent years that raised questions about police use of deadly force against black men.

Police say Ferrell wrecked his car on the morning of Sept. 14, 2013, went to a nearby house and banged on the door, apparently for help. The resident inside the home called police, and three officers responded. Investigators say one officer deployed his Taser without apparent effect on Ferrell before Kerrick fired 12 shots, 10 of which hit him. Kerrick was the only officer who fired his .40-caliber semiautomatic service weapon.

Kerrick testified that he repeatedly fired because Ferrell kept charging at him and he didn't think his weapon was even working.

Holding back tears and in a quavering voice, Officer Randall Kerrick re-created the events, at one point yelling "Stop!" and "Get on the ground!" to a nearly packed courtroom

Police training expert Dave Cloutier testified that Kerrick's decision to shoot Ferrell was consistent with the department's training.

Cloutier, who has served as an instructor at the North Carolina Justice Academy, said Kerrick was responding to a potentially dangerous 911 call: a report of a man breaking into a woman's house.

However, Police Capt. Mike Campagna testified that the shooting violated department policy. He said nonlethal force should have been used to subdue Ferrell.

Kerrick's attorneys have argued that Ferrell was moving quickly in the officer's direction. They say Kerrick opened fire because he feared that Ferrell was going to attack him and take his gun.

Officer Adam Neal, who was also at the shooting scene, testified that he never considered pulling a weapon that night and instead viewed the situation as one that would require physical force to restrain the subject.

Defense attorneys targeted Ferrell's condition at the time of the shooting, pointing to the fact that he had smoked marijuana and drank alcohol before the wreck that led to the deadly confrontation.

The Ferrell family has already settled a lawsuit with the city of Charlotte, receiving $2.25 million.

Ferrell was killed a little less than a year before an unarmed black man in New York and an unarmed 18-year-old black male in Ferguson, Missouri, died after separate violent encounters with police — cases that shined a national spotlight on how police departments treat minorities and sparked calls for widespread reforms. Protests and rioting followed Michael Brown's death in Ferguson and a grand jury's refusal to indict the officer.

Protests also followed the deaths of two unarmed black men after encounters with police earlier this year in Baltimore and South Carolina. Officers have been charged in both of those cases. Kerrick's trial, while packing the courthouse, has drawn little outside attention.

Unlike some other cases, the officer was arrested and charged about 12 hours after the shooting.