Suspects in this case attended a party at which they were under the influence of "goofballs", 1960's slang for barbiturates.
The "silent six" of this episode's title presumably refers to the neighbors who hear Susan Wolfe's screams as she is being beaten in her apartment, but do nothing to intervene or get help. However in the story there are only four such "earwitnesses": Linda Blakely, Professor Jefferson, Flo Oliver and Ron Peters. They are the only residents of the apartment complex shown listening during the attack (besides Joe Oliver, who does intervene only to become the murder victim), the only witnesses shown being interviewed afterward about the events, and the only witnesses shown testifying in court. No other witnesses appear in the story at any time, nor are any mentioned. Thus the "silent six" is actually only four people.
During the courtroom scenes, the usual defense/prosecution layout is reversed, with Mr. Mason and the defendant seated on the judge's left.
One of two shows in season nine to show 1966 Corvairs (Chevrolet's rear-engine compact), both are four-door hardtop sedans. In The Case of the Wrathful Wraith (1965), a bronze example is in the parking lot of the courthouse as Mason escorts Louise Selff out after an acquittal; in this show, Steve Drumm and Dave Wolfe are seen in a dark-colored example.
This episode's story is based, in part, on the then-current (but false) public perception of the Kitty Genovese case. On March 13, 1964, Genovese was raped and murdered in New York. At the time this episode was filmed, the widespread public understanding of the Genovese case was that while she was being murdered, many witnesses who resided in her apartment complex saw the event transpire and chose not to act either by intervening directly or alerting the authorities. This led to decades of the case being considered emblematic of bystander apathy and group inhumanity; however, this perception was derived almost totally from one largely inaccurate account of the murder that in the twenty-first century has been heavily debunked.