I took a look at the Web site you mentioned. What I saw was totally inacceptable: weird antisemitic claims, including the denigration of the Jews and the denial of the Holocaust. This constitutes a crime both in certain countries and in my opinion.  I take it very personally.  If what you said about the connection between the user and the nazi Web site is true, then even simply keeping this user's account around sends a wrong message. If this user is or was really connected to the Web site (I don't see any posts of the user right now, but the administration or the other users might), I vote for removing the user's account.