From: Rabbi Moshe Sofer
To: Rabbi Tzvi Avigdor
A Jewish man disappeared during travel, and a gentile murderer confessed before a judge to killing a Jew, later affirming his sentence at execution. A Jewish travel companion identified the victim as R' Yosef. The Chasam Sofer rules to permit the wife to remarry, finding the murderer's voluntary affirmation at execution superior to standard mesiach lefi tumo testimony, combined with the living companion's direct identification of the victim.
Source: Shu"t Chasam Sofer EH I §90