So about this post, should I share here the username so others could report him too?

That's the problem, SW-police says you must not name anybody no matter how heinous or what they do. Of course, it shouldn't be a matter of how many people report them, they can and will just get a new account, and if it happened in private messages there really isn't grounds for other people to report them. Ethically I feel it's cases like this where other people they may have friended should get to know what they're doing. I've seen people post screencaps with the username poorly masked out, so people can make up their own minds. I'm not saying that's allowed, though.