A US police officer who shot and killed a suspected shoplifter in a wheelchair, hitting him nine times in the back and side, has been fired from the police force.

Police in Tucson, Arizona, said off-duty officer Ryan Remington was working as a security guard in a retail area when 61-year-old Richard Lee Richards allegedly stole a toolbox from a Walmart supermarket.

Disturbing footage released by the department shows Mr. Remington meters behind Mr. Richards, asking him to stop. When Mr. Richards refused to stop his motorised wheelchair, Mr. Remington opened fire, shooting the suspected shoplifter in the back and the side.

Tucson Police Chief Chris Magnus said a Walmart employee had called Mr. Remington for help.

“According to the employee, he (Mr Remington) caught up with Mr. Richards outside as he fled the store and asked to see a receipt for the toolbox,” CNN quoted Chief Magnus as saying.

“Instead of providing the receipt, Mr. Richards brandished a knife and said, ‘Here’s your receipt.'”

Chief Magnus told a press conference he was “deeply disturbed” by his officer’s actions.

“His use of deadly force in this incident is a clear violation of department policy and directly contradicts multiple aspects of our use of force and training.

“As a result, the department moved earlier today to terminate Officer Remington.”

CNN quoted Mr. Remington’s attorney Michael Storie as saying the video did not tell the whole story.

Mr. Storie said Mr. Remington “attempted to de-escalate the situation” but Mr. Richards’s actions left him “no choice but to use deadly force”.

Watch the disturbing video below…