Hosted by “Dateline’s” Andrea Canning, “Dateline: The Smoking Gun” is a hunt for clues as detectives relentlessly pursue the critical piece of evidence that ultimately cracks the case. Each investigation is packed with twists — false leads, wrong suspects, dead ends — until police finally uncover the smoking gun and arrive at justice. Stories investigated this season include a disappearance involving a young film director, two prosecutors killed in a small Texas town and a serial killer who must be stopped before the next victim is murdered.