Ellery Queen - Season 1 - Eps 14: The Adventure of the Eccentric Engineer
Heeeeeeeeeeere's Ed. Ed McMahon, that is, who plays a once brilliant but now seemingly senile inventor who is murdered in his electric train workshop. This one's a toughie because it appears as though no one could have entered or left the workshop during the time in which the murder must have taken place.
About Ellery Queen

Title: Ellery Queen
First Air Date: 1975-09-11
Last Air Date: 1976-04-04
Status: Ended
Rating: 7.4/10 (from 39 votes)
Language: EN
Seasons: 2
Total Episodes: 22
Network: NBC
Genres: Mystery, Drama
Production Companies: Universal Television, Fairmont/Foxcroft Productions, Tom Ward Enterprises
Synopsis
Ellery Queen is an American television detective mystery series based on the fictional character Ellery Queen. It aired on NBC during the 1975-76 television season and stars Jim Hutton as Ellery Queen, David Wayne as his father, Inspector Richard Queen, and Tom Reese as Sgt. Velie. Created by the writing/producing team of Richard Levinson and William Link, the title character "breaks" the fourth wall to ask the audience to consider their solution.
Cast

Jim Hutton
Ellery Queen

David Wayne
Inspector Richard Queen

Tom Reese
Sgt. Thomas Velie