Google will not disclose the Bloggers information without a third party subpoena. I would like to put the individual on notice prior to commencing legal action.
If he is anonymous you will have to write to Google and ask them to forward, or you could post it on the blog. But you should get an attorney. If you sue you can subpoena the identity from Google.
We have had some success in stopping such abusive activities if we can show Google that the blogger has violated the terms and conditions of their use, put Google on notice of this abuse, meaning if Google now fails to stop the activity, they become liable for any further abusive activity.
Stanley Dale Radtke, Esq.
220 Montgomery Street, Suite 416
San Francisco, CA 94104
415-252-1234