What he did is called *harassment*, and is punishable by law. It's not a free speech matter, because the intent here was perfectly clear. He pleaded guilty. Feel free to disagree with prison as the punishment, though.
In a case he *didn't* plead guilty, the prosecutor would have to prove over any reasonable doubt that his intentions were malicious. Which would be pretty easy, as the evidence is there. Nothing this guy posted or did goes under satire either. It was done solely to cause severe distress.
You wouldn't use the free speech card on the right to bully someone in the workplace, or follow someone dead in their tracks for a whole day. It's harassment, stalking and/or antisocial behavior. That this was done via the Internet doesn't make any difference.