Sentence:  `` Unfortunately '' , says Chief Postal Inspector David H. Stephens , who has prosecuted many device <WSD>quacks</WSD> , `` the ghouls who trade on the hopes of the desperately ill often cannot be successfully prosecuted because the patients who are the chief witnesses die before the case is called up in court '' . 
Meaning of the word marked with <WSD> tags:  an untrained person who pretends to be a physician and who dispenses medical advice