When you're working on cold cases, it helps to have a loyal partner. Someone who sticks around as long as it takes to wrap the case. On Cold Case, Lilly Rush wouldn't find that perfect fit until her second try.

In the first episode of Cold Case, we meet Lilly's original partner Chris Lassing. Lilly dubs him "Lass," and right from the start, she and Lass do not see eye to eye on the time they need to put in to solve the crimes that have gone so long unsolved. Maybe it's because Lass has a wife and a whole life beyond the work, things we know don't necessarily interest Lilly. Whatever the reason the pair didn't quite jive, Lass doesn't last long, and here's the actual reason why.

Lass was played by actor Justin Chambers, who was just coming off of two hit movies when he was cast: playing D'artagnan in The Musketeer and Massimo (the guy Jennifer Lopez's character spurns) in the rom-com The Wedding Planner, both in 2001. It makes sense that audiences continued to want to see the actor in leading man roles, with love interests to track. And though on Cold Case he played a decent detective, he didn't add the tension that Danny Pino brought with Scotty Valens, Lilly's next partner who shows up two episodes after Chambers left the show.

No, what made more sense for Chambers was to join the cast of a quite different show: Grey's Anatomy. Offered the part of Dr. Alex Karev, Chambers left Cold Case for scrubs and love (including a scandalous plotline involving Katherine Heigl's character Izzie Stevens).

So it was out with "Lass" and in with Scotty, who not only didn't mind the long hours Lilly kept, but notably shows up at just the right time to save Lilly's life. With respect to Lass, maybe that's the kind of partner Lilly needed all along.