Filmed primarily on location, it's a time capsule of 1962 Los Angeles, including an empty Hollywood Bowl.
The helicopter used, N8417E, is a 1960 Bell 47G.
Douglass Dumbrille, in a technical sense, is playing himself: An aged character-actor once known for playing heavies in mainstream pictures (including several starring James Cagney) is now providing a cameo in a low-budget feature.
Part of the movie is shot at The Hollywood Bowl, but during the daytime and it's mostly vacant.
The "LT Building" where the crime occurs and is investigated, shown in exterior/establishing shots, is at 5455 Wilshire Blvd., Los Angeles, Ca. 90036.