Neighbours of Ian David Long described the man who shot and killed 12 people at a country music bar as distant in public but combative with his mother inside the suburban Los Angeles home the two shared.

Sgt. Ron Helus, the sheriff's officer killed in the Borderline nightclub mass shooting in Thousand Oaks, Calif., was a husband, father and veteran officer on the verge of retirement.

Thirteen people are dead, including a deputy sheriff and the gunman, after a 28-year-old man opened fire in a crowded country dance bar in Thousands Oaks, Calif., on Wednesday night, police said.