The proof is there if you bother to read it. Freeper Marc Costanzo is in real life Chad Castagana of Woodland Hills. A Chad Castagana of Woodland Hills was arrested for mailing white powder letters to various leftists. Now maybe there's more than one anti-leftist Chad Castagana in Woodland Hills. I seriously doubt it though.
I did bother to read it. It said they were 'convinced' but I didn't see anything I would have called 'proof' in the article.