(Reuters) - The Los Angeles County sheriff vowed on Sunday to thoroughly investigate the fatal shooting of a black man by policemen who said the suspect refused to drop his weapon, after a video posted online appeared to show him crawling away.

Two unidentified Los Angeles County Sheriff’s Department deputies on Saturday killed Nicholas Robertson, a 28-year-old black man, in Lynwood, outside the city of Los Angeles, the sheriff’s department said. Officers said he had failed to comply with orders to drop his gun when they confronted him in front of a busy gas station.

The shooting was the latest to draw attention at a time of heightened scrutiny in the United States over police use of lethal force against unarmed black people. Over the past year, protesters have taken to the streets across the country to demonstrate against the police. Most of the protests have been peaceful, but some have turned violent.

“We understand the significant community concern anytime the police are involved in the use of deadly force,” county sheriff Jim McDonnell said at a news conference.

“We owe it to the family, to the public and the justice system to be thorough and deliberate” with the investigation, he said.

Deputies responded after receiving several 911 calls about shots fired in the area, said Steven Katz, an official with the sheriff’s homicide division said at the same news conference.

The sheriff’s department also said it had witnesses who had seen the suspect turn and point a gun at the deputies before the shooting.

The deputies fired 33 shots at Robertson, who was pronounced dead at the scene, where a loaded handgun was recovered, Katz said.

In a cell phone video posted online by KTLA, a news station in Los Angeles, two officers are seen shooting a black man who is walking away from them. After the gunfire ceases, the man is seen crawling on the ground away from the officers, who open fire on him again.

“In this modern age of cell phone video and instant analysis on the Internet, I would ask that we keep in mind that a thorough and comprehensive investigation is detailed and time intensive,” McDonnell said in the statement, although it was not clear if he was referring to the same footage.

A crowd of about a dozen people protested against the police at the scene after the incident on Saturday, KTLA reported.

“When they shot him in the shoulder and I see him falling … that’s injustice, for me,” Robertson’s mother-in-law Pamela Brown told KTLA.