Why William Petersen Decided To Leave CSI

The hit police procedural "CSI: Crime Scene Investigation" was seemingly unstoppable as the 2010s approached. While the show's viewership peaked with Season 5 in 2004 and 2005, it was still running roughshod over the airwaves a few years later. Season 9 of "CSI," for example, was the most-watched drama of the 2008-2009 television season — and that year's fourth most-watched show overall. By that point, the police drama had also spawned two similarly successful spinoffs with "CSI: Miami" and "CSI: NY." With that in mind, fan-favorite original "CSI" lead William Petersen may very well be the poster child for "going out on top," as it was also around that time he decided to call it quits. All these years later, some of us are still wondering what happened to Petersen and what exactly prompted him to leave such a successful program in the middle of its run.

In July 2008, three months before the premiere of "CSI" Season 9, the news broke that Petersen's Gil Grissom would be bowing out of the series, though Petersen himself would remain attached to the show as an executive producer. Petersen's final episode as a regular cast member, "One to Go," aired in January 2009. That same month, the actor explained his departure during an interview with Entertainment Weekly, and his specific reason for leaving may surprise you.

In his interview, Petersen confessed his fear that "CSI" was making him complacent. ”The reason I'm leaving is because I'm afraid I'm becoming too comfortable,” the "Manhunter" star said (via CNN). He added, "It's 'CSI' — they pay me a lot of money, and I don't have to work very hard anymore. I've got it all figured out. And I just realized, God, as an artist, I'm going to atrophy. You do anything for nine years, it becomes somewhat rote. I didn't want to be on the show [just] because they were paying me money and I liked the money. ... It was too safe for me at this point."

William Petersen didn't spontaneously decide to leave "CSI." As he told The Hollywood Reporter, "This had been coming for years. The decision wasn't made overnight." He had even planned his next job before leaving, a small two-person play in Chicago, with Petersen hoping to inject new life into his acting career by pivoting back to the theater. He also made it clear that he felt he had left it all on the table with his "CSI" character, Gil Grissom. ”I won't miss Grissom. It was a complete life for me that's reached its end," he told Entertainment Weekly. "And I hope that the audience won't miss him either."

This may have been wishful thinking on Grissom's part, as many fans were not too happy about Grissom's exit. According to an AOL poll conducted in late 2008, almost one-third of them even vowed to stop watching. That figure turned out to be somewhat accurate, considering the show lost a whopping seven million viewers leading into its next episode, one week after Petersen's departure. Indeed, while "CSI" remained popular enough to last another six full seasons without him, ratings did begin to slide following Grissom's farewell.

Mind you, in addition to remaining aboard as an EP, Peterson did return to the "CSI" franchise as an actor on several occasions. In fact, among "CSI" guest stars like Meghan Markle, Petersen was probably the audience's all-time favorite.  He made a brief guest appearance in the Season 11 episode "The Two Mrs. Grissoms," followed by two voice-only appearances in Season 13. Then, of course, Petersen made his grand return as Grissom for the "CSI" finale film, "CSI: Immortality," which aired in September 2015. Years later, in 2021, Peterson once again reprised his role as Grissom for the sequel series, "CSI: Vegas." However, he only appeared in the show's first season, having declined to sign on for any additional episodes.

"CSI: Vegas" would go on to run for three seasons in total through 2024. Not long after, in November 2025, Peterson decided to retire from acting altogether. He confirmed to People, "I just don't have the ego to go get in front of cameras anymore." Departing "CSI" seemed to be the first step along that path.