If it was a cold, calculated crime I would expect the killer to choose a more efficient weapon. To bludgeon somebody to death you would need to get very close to them, very likely involving a violent physical struggle. It would be difficult to do that without leaving substantial forensic evidence behind. Why take the risk? It makes no sense. Also, Julia worked as a police community support officer. Do you really think her work would likely have made somebody want to kill her? How often are PCSOs murdered because of their work? It’s the stuff of fiction, not reality.