You HAVE to fall on boilerplate or you will be crucified, by your lawyer if no one else. You just have to pick the right boilerplate:
If what you say has happened, that is a terrible tragedy. We will be conducting an internal investigation of the matter. Justin.tv in no way condones comments of the nature you have described. If we find that someone has breached our acceptable comment policies, we will deal with it as harshly as allowed to by law.