Let us consider the case of Conan Wayne Hale. This is a description of the crimes of which he was convicted, as posted on a State of Oregon web site:
“In December 1995, over the course of about two weeks, Conan Hale and Jonathan Susbauer committed two burglaries, sexually assaulted a young couple, and murdered three teenagers in a wooded area outside Eugene, Oregon. Hale later was charged with aggravated murder and various other offenses in connection with those crimes. The jury found Hale guilty of most of the crimes charged, including 13 counts of aggravated murder, and the trial court sentenced him to death. On review, Hale raised multiple assignments of error regarding pretrial rulings and the guilt and penalty phases of his trial. In a unanimous opinion, the Supreme Court affirmed seven of the aggravated murder convictions and the sentences of death thereon, and it reversed six of the aggravated murder convictions and vacated the sentences of death on those convictions.”
Obviously, these crimes are worse than those in the scenario of the OP.
You may recognize the man’s name. He was accused of these crimes and incarcerated in the Lane County Jail in Eugene, Oregon, where his confession was later heard by a certain Fr. Timothy Mockaitis. Unbeknowst to Fr. Mockaitis, where the confession was secretly taped by the sheriff of the jail, with the intention of using the tape as evidence at trial.
The Archdiocese of Portland and Fr. Mockaitis fought to have the tape destroyed. In a statement to a judge in the case, a lawyer for the Archdiocese stated:
"It is allowed under canon law, the rule which governs the Roman Catholic Church, for a penitent to speak outside the sealed confession as to what occurred; however, the penitent cannot release the priest from his inability of testifying in church court nor in civil court about what occurred within the context of a conversation between himself and any particular penitent."
Under no circumstances may a priest disclose what is revealed to him in confession. Period. He most absolutely cannot tell the police or a judge!! It is the position of the Church that it would be a violation of his right to exercise his religion to make any law compelling a priest to break the seal of confession for any reason. If such a law existed, a priest would be morally bound to ignore it. We may not even ask a priest to reveal something about our own confessions to a third party. It is strictly forbidden.
Among the religious bodies that contributed friend of the court briefs in support of the Church’s position on the matter were the American Jewish Congress, the Church of Jesus Christ of Latter-Day Saints, the Baptist Joint Committee of Public Affairs, the Evangelical Lutheran Church in America, the Commission on Social Action of Reform Judaism, the General Assembly of the Presbyterian Church (USA), and the Christian Legal Society, not to mention, of course, the US Council of Catholic Bishops. IOW, the Catholic Church is not alone in believing that a penitent ought to be able to expect absolute confidentiality in this case.
I have heard Fr. Mockaitis speak on the matter, and he was deeply grieved that it was even implied that he might ever break the seal of confession for any reason whatsoever. There was no indication whatsoever that even a multiple-murderer, if he is contrite, might not receive absolution.
I cannot find it in Fr. Mockaitis’ book, but if memory serves correctly, during the time when the Polish government started bugging the confessionals in Poland, under the suspicion that the Poles were using priests to send secret messages, the priests were given the authority to absolve sins that were not verbalized to them! So sacred is the seal that it was preferable to absolve a sin, not knowing what the sin was, than to risk having the seal violated.
Keep in mind, though: Being absolved of a sin removes any eternal punishment due to the sin (keeps the penitent out of Hell) but does NOT necessarily remove all temporal punishment (the rehabilitating pains of Purgatory). The penance given by the priest in the Sacrament of Penance is not guaranteed to remove all temporal punishment, either.