[xwiki-users] User info in mysql database

I'm having an issue where we can't delete users from our Xwiki. There are a group of users who must have had a document or table related to them deleted from some reason. When we go to delete a user, it looks like it's been deleted, but when we go back and refresh the user list, the user pops up again in the userlist. We're trying to delete these users in the database directly, but we would like to know what tables/fields are used and what their relationships are. If we can find these out, it would help out immensely. Sam