I guess if I was to answer the original question given the additional facts my answer would be:

If you know he is doing wrong, and your conscious, tells you to act. Then, yes turn him in. But to so without the bravado of calling attention to yourself. Turn him in on a tip line anonymously. To bring attention to yourself in his "neck-of-the-woods" only brings possible retribution and that's not gonna be good for anyone!