Ten years ago a friend of mine committed a crime. He helped a homeless man carry a computer screen to sell it for drugs, even though he himself never broke in but helped carry it from the outside. No harm to any one was done as it was empty and just after midnight. Anyway, he was saved at afterward and has enjoyed a fairly gracious Christian life with ups and downs and got married and has a child. He is now tormented by guilt and anxiety about what he did 10 years ago, and it's not helping him live his life. Should he confess what he did ten years ago or trust God and move on?
I disagree with the idea that no one was harmed. Clearly the person who was robbed was harmed. Helping to commit a crime is no less a sin than directly committing the crime. "Do not lay hands on anyone hastily, nor share in other people's sins; keep yourself pure" (I Timothy 5:22).
I assume your friend was baptized after he participated in this crime, so he would be forgiven by God of it. A part of becoming a Christian is repenting of your past sins (Acts 2:38). While sins cannot be undone, sometimes it is possible to correct some of the damage done by our past sins. Here I would suggest that he send some money to the victim anonymously with a note explaining that he had once helped with a crime and he is sorry to have caused the harm. If he doesn't know who was robbed, he could give a similar amount of money to a charitable cause that helps out victims of crimes.