The final moment of Gil Grissom’s “CSI” career - and the surprise first moment of the rest of his life - were in the planning stages for two years.

That may be why the closing scene of Thursday’s episode of “CSI” was so satisfying. Yes, we are going to discuss spoilers here, so run to your DVR or cbs.com and get caught up. We’ll wait.

The departure of William Petersen’s character from in front of the camera was mapped out in long conversations between two of the show’s two executive producers, Petersen and co-star Jorja Fox, according to Carol Mendelsohn, one of the showrunners on “CSI,” who has been overseeing production of the show since episode one.

“The initial discussions began during the miniature killer storyline,” said Mendelsohn in an interview on the “CSI” set this week. “We knew at that time that Jorja (Fox’s) character was going to move on,” Mendelsohn said, “and we discussed what that would mean to the relationship.”

That story arc, which dominated the show’s 2006-2007 season, involved the hunt for a serial killer who left behind perfectly detailed miniatures of her crime scenes. At one point, Fox’s character, Sara Sidle, was kidnapped by the killer, and that experience was cited in her eventual departure from ‘CSI’ last season.

Sara and Gus had been a romantic item since year four of ‘CSI.’ Viewers seemed to like the idea of these two in love, though many reacted badly when the affair went away for nearly two years only to reappear suddenly - some thought it a shameless ploy at a time when “CSI” was getting its first serious ratings challenge in years, from ABC’s soapy “Grey’s Anatomy.”

When last seen on the show, Sara was leaving to work on her personal issues. Well, apparently she worked through them just fine, and sent word to Gus to come see her in the rainforest of Costa Rica. There the couple shared a long moment of passion as Thursday’s episode went to black.

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And then, in the closing scene, Grissom is walking through the thick brush in Costa Rica when he lights upon an exotic bug sitting on a leaf. He stops to admire the insect for a moment … then marches forward into the arms of Sara.

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