LOS ANGELES — A medical examiner testified today in the murder trial of Christian Karl Gerhartsreiter that Gerhartsreiter’s alleged victim, John Sohus, died after being struck at least three times in the head by a blunt object. “It is a significant amount of force. It wasn’t a light tap. Any one of these three blows would have rendered him unconscious,” said Frank Sheridan, a forensic pathologist and the chief medical examiner for San Bernardino County.