My thinking has always been that, if this was a motive, the killer was not someone who failed to make the cut THAT year. It could likely have been someone who failed to get into residency sometime in the past, perhaps several years ago. This festered while they blamed the Hunters or CU for their perceived failure in life.
From what I know, the murders showed evidence of medical skill. The knives were left in their throats to minimize bleeding (less chance of leaving the house covered in blood). Of course this may also be a sign of a professional hit job.
If you think about it; the son of the then head of a Pathology department is murdered in his home, the killer entering just after he came home from school, the scene is as one OPD detective said, "almost pristine." To me that suggests a strong possibility of a connection with someone in the Doctrs' past, perhaps a medical or CU connection. It does NOT suggest the act of a prowler caught in the act or of a deranged psycho. This guy was good; very good.