Here's one for you... In 1997, I was in charge of several large repair facilities. I had a terminated employee (a troubled individual) call me to tell me that he witnessed my Shop Mgr, Shop Foreman and two Shop supervisor's smoke weed on New Year's Eve. He told me that if I did not take action that he'd go to the press and report it. I called HR who in turn got Legal involved. Legal said that I could not just test these 4 guys and that if I did test, that needed to test the entire shop, or 53 employees. HR concurred & encouraged me to do so. But I didn't want to succumb to his threats and I had some great long time employees, many nearing retirement. To test them would have been foolish and also embarassing for them. We had never tested before. So, I chose to ignore his threat. I called his bluff and never heard from him again. Sometimes you just have to do the right thing and hope for the best.
Unfortunately, in today's world, that troubled, terminated employee, I would consider to be a serious threat and a candidate for the type to return with a gun. Today's a different world than even in 1997.