Would you have shared this information with your boss?

A while back, a friend of mine and I had an internet message board. We had issues with a couple of trolls who posted flame bait, caused trouble with other members and badmouthed our board and us throughout the site. Before too long it got very out of hand and we were forced to ban both of the members. Fast forward five years. I have moved to a new place – a city where I know for a fact this troll lived. I also knew the troll’s real first name, and a few of their interests. The place where I worked hired a new employee with the troll’s name. I didn’t think much of it until I met the employee and they seemed to have many of the same interests the troll shared on the board. I asked straight out and sure enough, it turns out this person was the troll. The odds are astronomical I know, but the troll knew all about the board, the board’s members and admin and all the things that happened without me saying a word. I never said anything to anyone at work. Now that the person has left my place of employment I told one co-worker who was absolutely convinced I should have told the boss. What do you think? Would you have shared the information or kept it to yourself?