The simplest answer is usually the right answer. Who had done harm to JBR's head in the past? Who could sit down and enjoy a snack in the kitchen? What are the odds of the previous harm to JBR's head being an accident? How many people do you know that have injured anyone with a golf club, other than Michael Skakel?
Past behavior is the best predictor of future behavior. Burke done it, the RN was Patsy's cover. Or not.
Sorry. I don't find that to be "the simplest answer". Fine if you do.