Emmy-winning John Lithgow played the character of Arthur Mitchell, a fan favorite killer who would emerge in the show's fourth season. Lithgow's character would at first become a sort of father figure to Dexter but when things go south for the two, Arthur Mitchell makes sure that Dexter's life is forever changed.
Details on Trinity Killer's role in the ninth season are known only by the writers for now but it's good to see that some path has been found to include characters from the hit show's past. Will Trinity Killer be the only character coming back? I hope not but fans, keep your fingers crossed.