It’s called “accessory after the fact”, and they wouldn’t be guilty of it if they report it, that’s the whole point of reporting it.

An accessory must generally have knowledge that a crime is being committed, will be committed, or has been committed. A person with such knowledge may become an accessory by helping or encouraging the criminal in some way. The assistance to the criminal may be of any type, including emotional or financial assistance as well as physical assistance or concealment.

I wouldn’t know, I don’t have an X account

Then they won’t know about the crime to begin with. The very act of listening to the confession and advising spiritual penance provides emotional support.

I was wrong, the priest is an accessory to the crime.

In the United States, a person who learns of the crime and gives some form of assistance before the crime is committed is known as an “accessory before the fact”. A person who learns of the crime after it is committed and helps the criminal to conceal it, or aids the criminal in escaping, or simply fails to report the crime, is known as an “accessory after the fact”. A person who does both is sometimes referred to as an “accessory before and after the fact”, but this usage is less common.

You’re right, having done some light wikipedia-ing, emotional support such that a priest provides would make him an accessory.

Psychiatrists are legally obligated to report knowledge of certain crimes that would otherwise be protected by confidentiality laws, I don’t see why priests should be any different.

Exceptions exist, like when practices are outright criminal in themselves

Aiding and abetting criminals is a crime.