I've finished the next chapter to Ashikabi no Shinobi. I'm going to read it one more time, then it should be up some time tomorrow as my Christmas present to all of you. Please look forward to it.
And now that my status update is out of the way, I figured I would give you a trope since I do not have any advice to give right now.
Guillermo: Jimena, Patricia, Patricia, Jimena, what does it matter? You know what? I would have killed to see your face at the exact moment when you heard that Patricia Longo was Jimena Benitez!
Not necessarily confined to a villain confessing a crime, sometimes it's just information someone had wanted to keep secret, or information that someone wasn't ready to share yet.
Type 1: The villain has the goody-goody face on, but someone has provoked him into a moment of rage, at which point the anger does the talking and, in a Moment of Weakness, the confession of the dastardly deeds spills out along with all the vitriol. Different from an Engineered Public Confession because the villain's mental state has rendered him/her temporarily unaware/uncaring that there's an audience. The audience may or may not have any idea there's going to be a confession.
Type 2: The most unfortunate kind of Accidental Public Confession comes from someone blithely blurting out something they thought the other party already knows.
Type 3: "Is This Thing Still On?" Somebody doesn't realize there's a live microphone to pick up their confession. See also some examples in Did I Just Say That Out Loud?.
See also You Just Told Me for when the confessor is tricked into believing the other person already knows, andEngineered Public Confession for when the hero secretly arranges and records/broadcasts the confession. May overlap with Easily-Overheard Conversation. I'll Never Tell You What I'm Telling You is a variation of this.