The CW is rounding out the cast for The Flash.

The network has enlisted Law & Order alum Jesse L. Martin to co-star in the Arrow spinoff built around speedster The Flash, The Hollywood Reporter has learned.

Grant Gustin stars as Barry Allen/The Flash in the pilot, which will be an origin story similar to what producers did with Stephen Amell starrer Arrow. Barry, who appeared in Arrow's two-part winter finale, is described as a Central City assistant police forensic investigator who arrives in Starling City to look into a series of unexplained robberies that may have a connection to a tragedy in his past.

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Martin -- who played Det. Ed Green for nearly 200 episodes on the Dick Wolf procedural -- will portray Det. West, an honest, blue-collar cop who is a surrogate father to Barry. A soulful, funny and caring father to Iris -- Barry's potential love interest -- West came up through the foster care system and took Barry in after his mother's slaying and father's imprisonment. He believes in Barry and supports his efforts to prove his father's innocence.

The Flash project, from Warner Bros. Television, started as a backdoor pilot, with the third episode slated to air in the back half of Arrow's second season. The CW now will film Flash as a standalone pilot in a bid to launch "with a bang like we launched Arrow," CW president Mark Pedowitz told reporters last week at the TCA winter press tour.

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Arrow co-creators Greg Berlanti and Andrew Kreisberg as well as director David Nutter are behind the potential spinoff. Berlanti, Kreisberg and DC Entertainment's Geoff Johns -- a writer-consultant on Arrow -- will pen the script for Warner Bros. Television. Nutter -- who helmed the Arrow pilot -- will also direct.

Martin's TV credits include an arc on the second and final season of Smash and The Philanthropist, Broadway's Rent and its subsequent feature-film adaptation. He next stars as Marvin Gaye in the upcoming biopic Sexual Healing. He's repped by ICM, McGowan Management and Kraditor & Haber.

Email: Lesley.Goldberg@THR.com

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