Story highlights Officials identify the gunman as 28-year-old Nicholas Robertson

He reportedly walked through a residential area, firing several times

(CNN) Los Angeles County officials are investigating the shooting of a man killed by deputies who fired 33 rounds.

Footage released by the Sheriff's Department showed Nicholas Robertson, 28, walking down a road in Lynwood on Saturday morning carrying a gun in his left hand.

Witnesses reported seeing Robertson behaving erratically and shouting expletives, Los Angeles County Sheriff's Capt. Steve Katz said.

Katz said at one point, Robertson walked into a pizza store carrying the gun and left.

At least six businesses or residents called 911 to report the gunman.

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