Boyfriend Legally Screwed Over?

My boyfriend was convicted of felony grand theft auto when he was sixteen for breaking into an auto dealership. He admitted his wrongdoing and is gladly paying for it. But his cousin saw his criminal record as a scapegoat. His cousin destroyed private property wearing my boyfriends shoes and then lied on the stand and said that my boyfriend committed the crime. My mom in law is very charitable and helped raise his cousin so naturally when my bf was too big for the shoes they were given to his cousin. This all occurred when my boyfriend was a minor before I met him. There was insufficient circumstantial evidence in the case involving the property damage and legal misrepresentation. My boyfriends family was very poor and he had to be appointed an attorney. His lawyer never appealed even though my boyfriend had a clear alibi since at the time he was on house arrest with an ankle bracelet for the crime he actually committed! Its been over two years since he was convicted and given a judgement (the amount is blown way out of proportion 20,000 for defacing a rusty shed in a scrap yard with spray paint). He didn't think he could fight it and just accepted this conviction. His cousin is now a member of a dangerous gang in town and he is an upstanding citizen who volunteers for Teen Court (gives teenagers an alternative by letting their peers dole out punishment) and is currently attending college. What if anything can we do? Because I am having trouble accepting that there is no way to fix this broken system.