No, he sacrificed himself for the sanctity of the confessional, the most solemn binding obligation that any man can have.
St. John Nepomucene is especially the patron of priests who have died to protect the Seal of the Confessional. Note the cherub with finger to lips - St. John was tortured and then drowned for refusing to reveal to the King of Bohemia what his Queen had said in confession.
He no doubt welcomed this holy priest into Heavenly glory. "Faithful unto death."
The Vatican (or perhaps a diocese or parish with this saint as their patron) ought to purchase this book and give decent repose his the earthly relics.
So if you hear a confession of murder, you are obliged to let it happen? Read Romans 1 last verse. He is as guilty as the murderers if he did nothing to stop it.
I think the Catholic church has already gone through this several times in the past. If you hear of a child being tortured and murdered, you MUST tell someone. If you know of any crimes being confessed to, you must reveal it. If someone is running around on his wife, that's different. If someone wanted to kill Hillary, you must say something even if you don't vote for her. It's called "right and wrong." Taking an oath to hide crimes is a cult indication. I wonder how many priests are in Hell for protecting the mob?