Chometz she’ovar olov hapesach is a kenas, so in circumstances where a person did what he was supposed to do Chazal did not punish him.
The Noda Biyhuda says if someone’s chometz was stolen before Pesach and then it was recovered after Pesach, he can use it because he did nothing to be punished for. He says when the thief says “harei sheloch lefonecho” it means “go ahead and use it”.