The setting that escaped from the Vatican is actually a conflation of verses set by Gregorio Allegri around 1638 and Tommaso Bai (also spelled "Baj"; 1650–1718) in 1714.
tl;dr: The pope is a dick. He had a wonderful piece of music written, and then told everyone that they couldn't listen to it! So you know what good old Willy Mozart did?That motherfucker went to the sistine chapel to hear it performed, when home and transcribed it word for word. Therefore, Mozart is now the king of TPB! Mozart has successfully trolled the catholic church.