NBC experimented with a mystery/game show hybrid in the spring of 1979. Unfortunately, it might've been ahead of its time.
Whodunnit? was coupled with Highcliffe Manor on Thursday nights for about a month, as NBC was struggling to find hit series. Tonight Show announcer Ed McMahon served as host. McMahon was no stranger to game shows, having last MC'd Snap Judgment, a daytime game, in the 60's.
Unfortunately, complete episodes are hard to come by. We have just this sample clip, with guest star Eve Arden ("Grease") and panelists Barbara Feldon (ex-Get Smart) and Vincent Baggetta (The Eddie Capra Mysteries).
McMahon would recover from this failure and land another hosting gig, one that lasted for nearly a decade--Star Search.