Does a guardian's subsequent admission of error invalidate the Qasamah (oath-taking)?

Primary text

If the guardian of the slain person states after taking the Qasamah that he was mistaken, or that he unjustly accused the defendant of murder, the Qasamah is nullified. Consequently, the guardian is obligated to return whatever was taken as compensation because this subsequent statement constitutes a confession against himself, and his confession is accepted. Similarly, if the guardian claims what he took was illicit ('haram') and clarifies that he meant he lied in his initial accusation, the Qasamah is also nullified.