Liam Aiken would be a perfect Henry McCarty, Billy the Kid

I was watching an episode of Law and Order and noticed Liam Aiken. I remembered that he has been in several episodes, always portraying sensitive, intelligent young men and kids.
I was talking to a historian and we both agreed even when they were close to the facts, like Gore Vidal's Billy the Kid, there was something wrong. They never got Billy right. Billy was actually very skinny and incredibly smart. Val Kilmer was actually way too big a guy for the role. Though a great actor, he was too far away from the real Billy.
If someone could tell the truth, it would make a great story, but would require a great actor.

What do I mean. I have never seen a version of Billy's life which includes the fact that the DA who prosecuted him was a murderer. He had actually murdered the Chief Justice of the New Mexico Supreme Court.