My suggestion is that the Vatican establish a program whereby men are sent undercover to the various seminaries.
SD
I once read a non-fiction account of a PI investigating a missing young boy. The PI established a link to the "gay scene" in a small town, but there was no way to follow up the link because to get access to the gay scene you have to actually prove yourself to be gay and willing to do the things those guys do... (The PI couldn't make progress until he consulted with a gay PI, who did go in and fit in. Eventually, with the help of the inside guy, the missing boy was tracked down and returned to his family.)
In order for a Vatican undercover guy to win the trust of the scum he'd be investigating, he'd have to be willing to do the same stuff the scum does to prove himself trustworthy...
Mark W.