Darkness at Pemberley

Detective Inspector Buller is called upon to solve two mysterious deaths. A college professor has been murdered in his room. He was overheard by two witnesses starting a record player in his room, but shortly after he does not answer his phone, and is later found dead. Nobody entered the room in the meantime. Inspector Buller is able to solve the mystery, but cannot find sufficient evidence to convict the clever murderer. The murderer then disappears, and if you want to know what happens next you know what to do.