In one of Magnum's voiceovers he refers to Luther's colleagues as being like, "something out of a Sam Spade movie." Elisha Cook Jr., who plays Icepick, was in the most famous Sam Spade movie of all, the classic film noir, The Maltese Falcon (1941), in which he plays the hot-headed punk who killed Floyd Thursby and Captain Jacoby, and torched Jacoby's ship.
The letter to Luther and the ransom note are both printed on a 9-pin dot matrix printer using the standard Epson sans serif font. This story aired was about a year before the first mass-produced laser printers hit the market, which means that the example of print shown represented the state of the art for desktop publishing at the time.
This episode is the only time that the internal monologues of two different characters were combined, with Magnum's internal monologue serving to comically finish the sentence of Luthor's internal monologue.
In the voice-overs for a great many episodes, Magnum talks about an imaginary book he would like to write about how to be a private investigator. A biting irony is the Luther Gillis, who is as hackneyed, corny, overbaked and narrow-minded a PI that one could imagine, actually writes one (which was first seen in the first Luthor Gillis story), while Magnum, who could write a truly superior book, never does and barely ekes out a living.