Robert Knepper guest-starred as Internal Affairs Detective Rex Coughlin in "Pono Kaulike" (Episode 18, Season 5). He had Danny arrested for the murder of drug cartel boss (and CIA agency asset) Marco Reyes, while also booking Chin for tax evasion. Unfortunately, we won't be seeing Knepper as Coughlin again on Hawaii Five-0. He was killed by Gabriel Waincroft at the end of the episode.
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