Christopher Meloni is a fantastic actor, but he also qualifies as a "that guy" actor. By which we mean, every time he shows up on screen you say aloud, "Hey, it's that guy," and then promptly forget to look up his name on IMDb.
Six months later, you see him again, exclaim that it is indeed that guy, and forget to look him up.
In 12 Monkeys, Meloni plays Lieutenant Halperin, who is definitely a "that guy" character. Halperin is tasked with investigating Dr. Railly's abduction by James Cole. Halperin questions Railly about the abduction, and we're pretty sure Railly is thinking the whole time, "Hey, I know this guy."
During the interview, he not-so-subtly suggests Railly may be suffering from Stockholm syndrome. Later on, he calls her to update her on the case.
And that's that. Halperin disappears from the film after that, never to be heard of again. And Railly, busy with other things, forgets to figure out where she's seen that guy before.