Does the seal of confession extend to bystanders? A Catholic priest cannot reveal what someone has told him in confession. If he does reveal it, he will be defrocked and punished.

If a different Catholic than the priest unintentionally overheard the confession, and learned of something important, like a murder. Would the bystander be allowed to reveal what he had heard? Does the answer change if the bystander is also a priest?

Of course, a priest who received a confession of a murder would recommend that the person confessing should give himself up to the police. But assuming he refuses to do that, what would be expected / permissible?

This is a hypothetical question, but in the centuries since the seal of confession has existed, this must have come up.
Does the seal of confession extend to bystanders?

The short answer is yes.

No one may reveal what is said in confession.


  Another interesting side to this question is the obligation of the laity to uphold the seal of confession:  An interpreter needed for someone to make a confession or anyone who gains knowledge of a confession (such as overhearing someone’s confession) is also obligated to preserve secrecy (Code of Canon Law, #983.2).  For such a person to violate the secrecy of another person’s confession is a mortal sin and warrants “a just penalty, not excluding excommunication” (#1388.2).  Moreover, a person who falsely accuses a priest of breaking the seal of the confession incurs a mortal sin and perhaps other canonical penalties, including excommunication.
  
  Clearly, the Church regards the seal of confession as sacred.  Every person– whether priest or laity– must take the obligation to preserve the secrecy of confession absolutely seriously. - Can the seal of confession be broken or the secrets ever be revealed by priests?