CHARLESTON, United States (AFP) — A white former US police officer was sentenced to 20 years in prison Thursday over the fatal shooting of an unarmed black motorist.

The death of Walter Scott in April 2015 was one of the most shocking in a series of high-profile US police shootings, often involving minorities that have deepened tensions and added to distrust between officers and the communities they serve

Michael Slager, who worked for the North Charleston police department, was charged with murder in state courts, proceedings that ended in a mistrial last year.

But in May, he pleaded guilty to o6ne federal charge of depriving Scott of his civil rights by using excessive force while carrying out his duties.

On Thursday, US District Judge David Norton said the offense involved the underlying crime of second-degree murder.

The former policeman “acted with malice and forethought,” said Norton, “shooting an unarmed and fleeing Walter Scott.”

Slager then gave authorities false information about the circumstances of the shooting, the judge added at the sentencing hearing in a Charleston federal court.

The former officer shot and killed the 50-year-old Scott on April 4, 2015, in North Charleston when Scott fled his vehicle after being pulled over for a broken brake light.

Slager claimed he had acted in self-defense, saying Scott tried to attack him with his own stun gun. But video footage of the incident taken by a witness shows Slager shooting Scott in the back as he sprinted away from the officer.

Slager was then criticised for trying to stage a scene to back up his claim of self-defense, by placing his stun gun beside Scott.

He was arrested three days after the video surfaced a rare case of quick action in cases of police killings.