William Petersen on CSI finale, Sara and Grissom, and the legacy the CBS show left behind

It’s the end of an era: after 15 years on the air, CSI is coming to a close on Sept. 27 with a two-hour movie finale. The creators, producers, and cast met up on closing night of this year’s PaleyFest Fall TV Preview for a farewell salute panel on Wednesday (moderated by EW’s own Lynette Rice), and we caught up with William Petersen and some of his costars on the red carpet before the event to get their thoughts about the end of CSI.

“It’s like going home for Thanksgiving,” Petersen said about coming back to CSI to shoot the finale. “You get to meet your family again.” Petersen, who plays Gil Grissom, exited the series in 2009 but came back (along with Marg Helgenberger and Paul Guilfoyle, both of whom had also already left CSI) for this last hurrah.

“That’s the funny thing about CSI,” his costar Wallace Langham observed. “You can say you’re leaving, but you never really leave. Unless you’re dead.”

Petersen was cast as Grissom, the series’ lead, when the show first started. “I thought [creator Anthony Zuiker’s] idea was fabulous — and I didn’t know if we could pull it off,” he says of his decision to sign on way back in 2000. “I didn’t know what we could do with it, but I thought the idea was great. And I always thought that it would be interesting to see how we actually solve these crimes, and the people that actually do that work, that nobody ever knows about.”

“We always see the cops, we see the lawyers — that’s what television has always been,” Petersen added. “We wanted to see what happens behind those guys.”

Television has changed since CSI started: Now, forensic scientists are as significant a part of its landscape as those lawyers and cops. “We spawned a lot of other shows,” costar Robert David Hall noted, “and not just the [CSI spin-offs], but Criminal Minds and Bones and all these other shows borrowed a little bit of our template.”

The show’s impact has also been felt in other spheres. “It changed the way the courts look at evidence; it changed how lawyers have to present themselves; it changed how criminologists behaved,” Petersen said. “It made coroners popular! They could actually go to parties and have people talk to them!”

As Langham pointed out, CSI has also inspired more students to pursue forensics and criminology. “That’s a really great legacy,” he said, “because we need these people.”

When the show started, nobody knew what it would become. “It was a risk for CBS and it was a risk for us,” Petersen admitted — but it paid off for both parties. “I had no idea that the show was going to last for 15 years,” said Eric Szmanda, who plays Greg Sanders. “I don’t think I’ll ever have a job this long again, so I’m glad. I’m grateful for that.”

As CSI investigates its last grisly crime on TV and Petersen comes back for one final appearance, fans are wondering how the finale will address Grissom’s romance with Jorja Fox’s character Sara Sidle.

“Well, we do see each other again,” Petersen teases vaguely. “And talk to each other — as best we can, because we’re not very good at that.” But that’s all he would say. “It’s really a secret!”

The CSI finale, “Immortality,” airs Sept. 27 on CBS.

• ‘CSI’ finale: The cast looks back on 15 seasons

• ‘CSI’ first look: Gil reunites with Catherine and Sara

• Marg Helgenberger teases ‘CSI’ finale with behind-the-scenes reunion photos

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