Video has emerged of two police officers in southern California shooting at a man 25 times as he crawled away from them.
Civil rights groups want an independent investigation into the fatal shooting but police maintain the man posed a threat to the public.
Fatal shootings by police in the United States have been under the spotlight since violence spiralled in Ferguson, Missouri, and there are fears there will be a similar response to this incident.
Two Los Angeles deputies fired at least 25 shots at 28-year-old Nicholas Robertson after they confronted him outside a petrol station. They continued as he appeared to be crawling away.
Initial images were shot and released on social media by bystanders, but at a news conference police showed CCTV pictures from another angle to justify the officers' actions.
Police say married father-of-three Robertson had refused to drop his handgun, which they say they was recovered from the scene, and bystanders were at risk.
But as tensions rise in the community, police say they will conduct their own detailed and time intensive investigation.