Body camera shows moments before cop shoots unarmed man

A white US cop on trial for “murdering” a black driver in a routine traffic stop hopes video of the incident will clear his name but the lawyer set on proving his guilt says it is evidence of a “purposeful killing”.

Shaky video taken moments before the unarmed man was shot is set to prove critical in the murder trial of University of Cincinnati Officer Raymond Tensing.

Tensing has been charged with murder of 43-year-old Samuel Dubose on July 20, the Washington Post reports.

The officer claims he was dragged by Dubose’s car but prosecutors dispute that, saying that Dubose had already been restrained before being shot.

“It was so unnecessary for this to occur,” Joe Deters, the Hamilton County prosecutor, said at a news conference.

"I've been doing this for over 30 years. This is the most asinine act I've ever seen a police officer make, totally unwarranted.

“This office has probably reviewed upwards of hundreds of police shootings, and this is the first time that we’ve thought this is without question a murder.”

The officer says he feared for his life, but prosecutors have thrown that out the window saying the black man was unarmed and it was “an excuse for a purposeful killing.”

If convicted, Tensing faces life in prison.

He is only the fourth officer ever to be charged after a shooting, but already 500 people have been killed by police this year.

The incident comes less than two weeks before the first anniversary of the fatal shooting of 18-year-old Michael Brown on August 9 2014 which sparked mass demonstrations across the US.