As a general rule, a person who steals from another must reimburse the victim, paying the monetary value of the stolen item. There is, however, an exception to this rule: “When a person sins and commits a trespass against G-d by dealing deceitfully with his fellow in the matter of a deposit or a pledge, or though robbery, or by defrauding his fellow… and if he swears falsely… he shall repay the principal amount and add a fifth to it” (Vayikra 5:21-25). In other words, he must add an additional twenty percent (chomesh) to the value of the stolen item. He is also obligated to bring a guilt offering (korban asham).
In order for a person to be liable to this penalty, there are three conditions:
1. He must have stolen.
2. He must have falsely sworn that he did not steal.
3. He must have later admitted that he lied under oath.
May a victim decide to waive his right to the payment of the chomesh? According to the Mishnah in Bava Kamma, he may.
Given this explicit statement of the Mishnah, it is very difficult to understand the Rambam’s statement, “The chomesh and the [asham] offering are for atonement” (Hilchot Gezeilah 7:8).
If the payment of the chomesh serves to achieve atonement for the sinner, it would seem that the victim should not be allowed to waive it. Refusing payment would leave the thief without the ability to achieve atonement for his sins (swearing falsely as well as stealing).
One possible way to explain the Rambam is to say that the victim is permitted to waive payment of the value of the stolen item itself. Once he has done this, the additional fifth becomes irrelevant, as a fifth of zero is zero. If this happens, the thief does indeed lose his chance to gain atonement (Kovetz Shiurim). Alternatively, one might argue that the obligation to pay the victim is first and foremost a financial one. Once the thief fulfills this monetary obligation, he achieves atonement for his sins. Therefore, when he has no monetary obligation, even if it is because the victim chose to waive his rights, he achieves atonement (Avnei Nezer).
What if there is a case in which the thief does not need atonement? Is there still be an obligation to pay the chomesh? If the reason for the payment is atonement, then the answer should be no. Yet we know that if the thief dies before making the chomesh payment, his heirs must pay it (even though they do not need atonement). This strengthens our earlier suggestion that the obligation is first and foremost monetary, and taking care of the monetary obligation is what achieves atonement.