You might want to follow up on your complaint with the police, press them, nicely, but let them know you take an interest. Not many years ago, the police did not take these things as seriously as they do now. If you can, ask the police what you should do if the call comes again, what sort of info might be used to make a case/file and official complaint. Make are recording? Have someone listen in as a witness? I am glad you care about the people working for you. Good Luck!