When does Meursault realize that for the first time he was guilty? What is he guilty of?

I don't think Meursault really cared if he was guilty or not. In this case, the lawyer, with public support, goes in for the kill. The crime is Meursault's lack of morals and refusal to participate in a moral code, reflecting the quotation Camus gives about his hero. The man with knowledge of the Absurd does not give into the game or the program but acknowledges that his actions on Earth do not amount to much or matter for anything or anybody.