An evil from D.B. Russell and Julie Finlay's past will be back to haunt them in CSI: Las Vegas season 15, and the villain will give viewers a chance to explore the pair's Seattle relationship.

'CSI: Las Vegas' Begins Filming A 'Super Dark And Twisted' Season 15, Richard Speight Jr To Guest Star

Franklin & Bash's Mark-Paul Gosselaar is on board to play a serial killer and his twin brother for a season long arc, and the killer will be one that Russell (Ted Danson) and Finlay (Elisabeth Shue) put behind bars all those years ago. As Gosselarr's execution date approaches, a copycat killer strikes, calling his sentence into question.

As the case drags across the season, the two CSI's will head down memory lane.

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"It dredges up a lot of feelings - about what happened five years ago, where they were in their relationship five years ago," said executive producer Don McGill, according to TV Guide. "The relationship in the past informs the relationship in the present."

Could a romance be on the horizon? Find out more when CSI: Crime Scene Investigation returns to CBS this fall. Click the video below to see a preview of the series' latest episode.

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CSI: Crime Scene Investigation, Television, CBS