This is the first time in the series that a murder gun is an automatic pistol instead of a revolver. During the years this series was produced, revolvers were much more popular than automatic pistols.
In the swimming pool scene, a radio is softly playing a tune featuring a tenor saxophone solo. It appears to be the same tune that was used to accompany the fan dancers' performances in "The Case of the Fan Dancer's Horse" that aired three episodes earlier.