DATELINE WEEKEND MYSTERY SNEAK PEEK: While He Was Sleeping

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When a successful luxury car dealer is murdered in his sleep, detectives shift their focus to one of the victim’s lovers. With a lack of hard evidence, the investigation stalls until a year later when one lucky clue breaks the case wide open. Josh Mankiewicz reports Saturday December 9 at 9/8c on NBC. Airs Sunday December 10 at 10 p.m. on the West Coast.