Bava Kamma 109a Recovery – וצריך שיאמר זה גזל אבי

Teshuva requires confession, וידוי. For a sin against Hashem the confession is in private, but for a sin against another individual the confession must be made to him. Theft is both a sin against G-d and against man and needs an interpersonal confession even when the victim is no longer alive. Source Sheet