Could this present a legal problem?

• doctor of business administration

If I know something really bad about a person who is "admired" because he's a doctor, and posted a remark on his Facebook page about it, could I get into legal trouble (sued for slander)? This is NOT slander, it's absolutely Truth and I have proof. It just irks me that this person gives everyone the idea that he's an upright, good person....but the truth is he is EVIL. And he needs to be exposed for what he is. I've heard that it's only "slander" if it is NOT true. But posting it on Facebook (for all to see)......would that present a problem for me?

Additional Details

Actually this guy ("doctor") has a son who attempted suicide last month, thankfully he survived. But this "doctor" who was notified about this (his son), could NOT have been less interested. He did not even call his son. This son went through physical abuse as a child from this "man", so far as making him lick dog pee off the floor. This "man" also abused animals. When his dogs would dig holes in the yard (back yard, so no one could see) he would put ammonia into the holes and stick the dogs nose into it, choking the dog. This "man" has abandoned this son, and now with his 3rd wife, is trying to appear like a decent man to her grown children. It just irks me that he seems to always "shine", when I know his true character. IF I were to post anything on his FB page, no one there knows me. He lives in another State. And it's on his "Clinic" page, where his patients are lauding what a great doctor he is. B

Could this present a legal problem?