Mayf Nutter plays Hawkins' nephew who does his legwork, and is basically replacing Hawkins' cousin character, Strother Martin... this is one of three episodes (of eight total) that Martin isn't in.
Henry Jones appeared in Vertigo (1958) with James Stewart.
Judson Morgan also played a judge on an episode of Columbo... which this show shares similarities, and each episode were also considered a TV Mystery Movie as opposed to TV series episode.
James Stewart and Murray Hamilton appeared together in The Spirit Of St. Louis (1957), The F.B.I. Story (1959), and Anatomy Of A Murder (1959), the latter of which was an inspiration for Hawkins (1973), about a small town defense attorney against the odds.
The only film in which both James Stewart and Sam Elliott appear. And it's not a Western.