Peterson says he knows there are ways of finding out who this person is
Is this the same individual who can't figure out how to work his microphone on every single Interpreter podcast episode he participates on?
He's most likely, wrong. Unless the person doing it is a complete idiot, it should be trivial to hide their identity such that the police and FBI simply can't find them. On the chance the individual slipped at some point, it then becomes a matter of throwing resources at this problem vs. a real problem, like, a kidnapping or something. It's probably still in the arena of civil law, since it's just harassment and no explicit threats, and even if there were threats, I doubt it would be enough for the cops to care, especially considering the likely impossibility of tracking the person down. I had to go down this road a number of years ago to help a family member with harassment including actual threats from an ex-con, in real life, not hiding behind a proxy online, and it's pointless, LE simply doesn't care unless blood is drawn if it's not domestic. I couldn't even get the cops to let me file a report.
There is a reason why most of us just ignore or block unwanted electronic communications, rather than give the offender a platform.
But I realize in this case there is some serious psychology going on. In my opinion, and I'm just speculating here, this isn't about the person sending the emails. Decades ago, Mr. Popular, the captain of the swim team and unwanted student body president, suffered a defining moment when a bunch of kids yelled his name as they drove by him in their car. We don't even know if they harbored any ill-will, just that, to this point in his life, nobody had implored Mr. Popular in a manner that wasn't praising.
What if they were mocking him? For decades this has built up as we've been treated to the story several times; he was, and is, powerless to do anything about those kids in that car. And so now, his person sending the emails, is a proxy for those jeering teenagers. Maybe, maybe there's a chance to finally get even?