After he takes down Eddie Parker, Asten revels that he was an Airborne Ranger.
This was the first appearance of the recurring characters of government agents Brice and Niven.
Quincy refers to Ellery Queen (1975) during an autopsy early in the episode. Ellery Queen is a fictional character that first appeared in a 1929 detective novel, itself penned by two cousins under the pseudonym Ellery Queen. New novels - many ghost-written by other authors - were published right up until the start of the 1970s. The character was still well-known at that time, appearing in two movies and, most recently, a short-lived TV series in the decade before the Quincy episode was filmed.
The murdered Bulgarian defector that Quincy refers to was Georgi Markov.The poison used was enriched ricin delivered by an umbrella.
The Air France aircraft featured prominently at the start of the episode is a Sud Aviation SE-210 Caravelle III, a variant of the first successful rear-engined jet airliner. The particular aircraft seen was known throughout her career as Aquitaine, Guyane, and Guadeloupe, with the latter being the name she bore during filming of Quincy. Just 11 years old at the time, she was nevertheless withdrawn from use only three months after the episode aired. Nine months later, she was scrapped at Paris' Orly airport.