You could ask Facebook for the e-mail that the account was created with, but I highly doubt they'd give it to you for privacy reasons. Any other way to get information on the creator is likely illegal.
And no, there's really no way to prevent this. This ex-employee could easily make a new e-mail account if Facebook did block his (unlikely), and they aren't going to put a restriction on people registering with your name. Although if you could identify him, you could probably play his game.
