Advanced facebook question...?

[Colanth]

If you have VALID grounds (hints aren't) to suspect that he's going to harm you, get the police involved. (He can't harm you over the internet, he has to physically come into their jurisdiction, at which point they can arrest him.)

Hacking into Facebook would put YOU on the wrong side of the law. Justification modifies punishment, it doesn't negate the fact that you violated the law. (No one is going to risk federal prison for you.)