Justin Bieber
The singer played the troubled Jason McCann, who at first seemed to just be caught up with the bad guys. Turned out Jason was a baddie himself, and he ended up getting shot in a police standoff. Baby, no!
Joe Manganiello
The True Blood stud appeared as a creepy stalker ex-boyfriend—and killer.
Dakota Fanning
Way back in season one, the up-and-comer played one of two sisters whose parents and other siblings were brutally murdered. Daily Show funnyman Aasif Mandvi also showed up for the first time in this episode as Dr. Leever, a recurring fellow crime-solver.
John Krasinski
Before he found work at The Office, the actor portrayed the roommate of a stoner found dead in his Jeep.
Taylor Swift
The pop-country superstar was almost unrecognizable as a brunette teen whose motel-owner parents didn't pay attention to her until it was too late.
Jason Segel
Viewers briefly met the How I Met Your Mother star when he had a recurring role assisting Doc Robbins in the coroner's office.
Melinda Clarke
The Nikita siren's song played loud and clear in her recurring role as everybody's favorite dominatrix turned therapist, Lady Heather.
Jason Lewis
The Sex and the City star played a sleazy club owner who might be responsible for the death of a ganster's daughter.
Deborah Ann Woll
The True Blood vamp caught Nick Stokes' eye as a diner waitress...right before Warrick got killed. Eep!
Zachary Quinto
Before he was Sylar or Spock, the Heroes star played a chop-shop owner in a season-two ep.
John Mayer
The crooner appeared as himself, playing at a club where a rapist drugs Catherine's drink. Yikes! Time to find better venues, Johnny.
Katey Sagal
The Married...With Children matron turned Sons of Anarchy badass played a difficult sitcom star whose murder leads to no end of suspects. Fun fact: Two and a Half Men cocreators Chuck Lorre and Lee Aronsohn cowrote the episode.
Rachael Harris
The Hangover actress played Sagal's disgruntled costar in the episode.
Charlie Sheen, Jon Cryer & Angus T. Jones
The Two and a Half Men stars made a cameo in Katey Sagal's episode when Grissom and Brass' investigation went Hollywood Burbank.
Chad Michael Murray
The One Tree Hill stud played an arrogant actor—a movie star, for dramatic purposes—accused of a double murder.
Liev Schreiber
The Salt star had a recurring role in season seven as CSI Michael Keppler.
Kat Graham
The Vampire Diaries star played a girl whose brother was out for revenge after she appeared in a Girls Gone Wild-type video.
Michael B. Jordan
The Friday Night Lights star played a member of a rapper's street crew, who takes his fandom a little too far.
Douglas Smith
The Big Love star appeared on the show twice as teen Marlon West, whose genius younger sister helped both acquit and frame him—for two different murders.
Kyle Howard
The Royal Pains actor appeared as a victim who was killed after one wild night in Sin City.
Kristin Bauer
The True Blood babe appeared as a woman suspected of killing a surrogate mother.
Rascal Flatts
There was some animosity among the mock-feuding bandmates as one of the country rockers suffered memory loss after being electrocuted.
Harold Perrineau
The Lost star played a sex-offender turned preacher responsible for an exorcism gone wrong.
Rainn Wilson
Four years before The Office premiered, the three-time Emmy nominee was "Guy in Supermarket" in the first season finale back in 2001.