The killers commenced their bloody work at the former Mission San Miguel Arcángel after 8 p.m. Dec. 5, 1848, when Samuel Barnberry struck their host, William Reed, on the back of the head with an ax. By the time they were finished they had committed one of the most heinous crimes in California’s history, leaving behind a scene of such horror it is said to linger on in the form of screams coming from empty rooms, a woman in white wandering the ha…