(REUTERS) - Emotions are running high after California sheriff deputies shot dead a black man on Saturday (Dec 12).

They say 28-year-old Nicholas Robertson refused to drop his weapon, but some who saw videos of the incident posted online say the suspect was crawling away as he was fired at.

"They shot him in his shoulder and he was crawling", said Ms Pamela Brown, Robertson's mother-in-law.

"He left three kids behind, two daughters and a son. They could have tasered him, anything."

Los Angeles County Sheriff Jim McDonnell briefed reporters on the shooting on Sunday, saying he expected the scrutiny.

"The sentiment across America has been critical. That's why we've come out today to try to be as transparent as we can with the information we can share at this time."

Officials promise a thorough investigation into the incident.