An off-duty San Diego Police officer fatally shot his knife-wielding brotherFriday in apparent defense of himself and their mother during a fight at the family’s South Bay home, authorities reported.

The lawman, whose name was not immediately released, suffered at least four stab wounds during the fracas in the 300 block of Center Street in Chula Vista, according to police. He was taken to UCSD Medical Center in Hillcrest in stable condition, CVPD Lt. Fritz Reber told reporters.

The siblings were arguing shortly before 8:30 a.m. when one of them picked up several knives and reportedly began acting in a threatening manner toward his mother and brother, Reber said. The aggressor then attacked his sibling, who responded by opening fire, the lieutenant said.

The mortally wounded man, whose name also was withheld, reportedly had a history of “mental-health issues” and lived with his brother and parents at the apartment complex directly across the street from Chula Vista police headquarters, Reber said.

City News Service