If everyone were to tell the truth, there would be no need for trials. Malicious intent can influence the plaintiff, the defendant, the lawyer, the jury, and the judiciary.
When unclear lines exist between truth and falsehoods, stretched over centuries, there are bound to be extensive measures to protect both sides of the justice system. Every side will strive to defeat the guilty verdict. Money. Power. Influence.
It no longer becomes a question of who is innocent or who is guilty. Trials are a game of who gets what they want.