The real question is if he HAS set off tnt in any towns or on anyone's base, why has he not been dealt with? Killing people is completely allowed. blowing stuff up is not.
If you are trying to get mods to notice that he is a griefer, it would probably be a good idea to post some screenshots for some proof. You could also get some block checks to help out with the problem as well.
"If ignorance is bliss, then knock the smile off my face."
—Zach de la Rocha
"People should not be afraid of their Governments. Governments should be afraid of their people." -V
Though leowester may be a known griefer, he can't be banned unless someone actually catches him griefing and calls for a block check. Otherwise these are just rumors?