In the early 2000s, there was no touching the popularity of CSI: Crime Scene Investigation, the original series that launched a franchise that shot off TV and became comics, novels and video games, too. In its third through fifth seasons, the show stuck firmly at No. 1 in the Nielsen ratings, quickly and instantly spinning out into another series, CSI: New York, which debuted fall 2004.

Each new city the series explored featured crossover episodes, so fans always knew that all these crime dramas between different CSI shows were happening simultaneously, within the same TV universe. This kept fans tuning in to each show, to keep up with all their favorite detectives from Vegas, New York and Miami. But just before CSI brought us to New York, there was another crime drama that debuted on CBS, Cold Case. That series was set in Philadelphia, a city that CSI had not yet visited, and as soon as Cold Case became the next big crime drama to watch, it's no wonder writers started to wonder: Would it make sense for Cold Case to be set in the same time and fictional universe as CSI?

By 2006, Cold Case and CSI: NY had tied in the Nielsen ratings, and the fans of crime TV had spoken: They loved both shows equally. Those fans only had to wait until the next season for CBS to bring those two series together formally, during a crossover episode from CSI: NY's third season called "Cold Reveal." It was the moment it became official that Cold Case and CSI were tracking crimes simultaneously within the same timeline.

In "Cold Reveal," Cold Case co-star Danny Pino appears as Scotty Valens (detective Lilly Rush's partner from the second season on), investigating a murder that took place in CSI: NY's Stella Bonasera's past. It put the two shows directly in conversation, confronting one of CSI's stars with a cold case of her own and giving Cold Case detective Valens a reason to look into a CSI detective's past. It doesn't take a detective to figure out that crime TV fans would massively enjoy following along with a juicy case like that.