I like the "killer hidden inside the team" kind of plot and the shock with it.
I really don't mind spoilers.
Tell me what you saw is an example but preferably more involved than that villain.
Vincenzo
And kind of...He Is Psychometric (the killer is the ML's brother, a prosecuting attorney, who is working on the casr)
+ MouseJusticeWatcherStrangerTrinity of ShadowsBurning Ice
The Usual Suspects probably most famous example of such!
Not entirely sure if this counts but in My Lovely Liar the detective (Kwak Jin Hyuk) is hiding some crucial information that could otherwise help solve the case
There was Elementary, where sherlock Holmes former girlfriends ended up being professor Moriarity!