Why does Justine confess to a murder she did not commit?

Shockingly, Justine confesses to the murder, and expresses a wish to see Elizabeth, who asks Victor to accompany her. Justine tells them that she confessed to a lie in order to obtain absolution and avoid excommunication in her last moments. She does not fear death, and nobly spends her last moments in comforting Elizabeth and Victor. This only serves to heighten Victor's anguish, and he reflects that Justine and William are the first victims of his "unhallowed arts."