It first appeared to be an all-too-typical drive-by shooting in San Francisco's troubled Western Addition - distinguished only because it was witnessed by a member of the city's Board of Supervisors. But police now say the incident was far darker: an extreme case of vigilante vengeance involving a father and his 16-year-old son against a supposed street robber blamed for holding up the youth on the way to school. The 39-year-old father, after being summoned to the scene by his son, allegedly ran over the suspected robber in the family car and then urged his son to shoot the prone...