If this were me, I would be pretty open about it in my job. I would probably joke about it with my co-workers. I would certainly talk to my bosses and my bosses bosses.
If I were an executive and got a letter about one of my employees, I might talk to that employee. I wouldn't believe the letter, I would suspect it was just a rather nasty neighbor.
Talk to your boss and be open about what happened. And, talk to a lawyer (you may have a case against your neighbor).