Sonoma County investigators have officially closed a cold case homicide more than four decades after the crime occurred. Sheriff’s officials used advanced DNA testing to identify Oscar Chotos Bolanos as the suspect in the 1983 sexual assault and fatal stabbing of 31-year-old Robert Pangborn in Guerneville. Detectives tracked Bolanos to El Salvador after discovering he had been deported following an unrelated conviction in Los Angeles County. Whi…