Mod Cooperative

I would normally figure it out myself, but this one is different. I have a known troublemaker in my community. At the time when they apped I didn't know it was them. They had already sneaked one person by me, but I've been in a community with them before and I see the warning signs. They're already harassing one of my members into leaving so that they can bring in a former sl partner. I warned them and they simply told me that they were doing it IC and in not so many words told me I was even stupid for warning them. I don't know what I should do; just remove them? I've seen communities being ruined by this person before hand I enjoy this place far too much to let it crash and burn.