Legal Question in Employment Law in Illinois

This sounds like a pretty serious matter. How do you know that management has not "done anything"? Perhaps they have counseled him and written him up but I am surprised your company is not taking remedial/preventive action such as terminating him if the threats are continuing in nature. You should outline your thoughts and concerns in a letter and give this to your company's HR manager. Keep your letter professional and stick only to the facts of the situation. It will help if you can provide dates and specific examples of this person's conduct. Good luck.