Luigi Mangione

It's more likely that the idea of a "watch list" is obsolete at this point. Now they create elaborate records and psychological profiles of every person they can, domestically or abroad. They also likely track everyone's physical location as close to real time as possible.

Maybe that's how they actually caught Luigi. They caught him because they know everyone's physical location at all time. They just had to rewind the clock back a bit, see who was standing near Thompson at the moment of the shooting, and they instantly knew it was him.