This was easily the most creative and freshest of the detective series of the modern time frame from 1980 to 2020.
The show revolves around the regular cast, who pretty much stay in the background to the actions of guest stars. That's pretty much how most good TV action shows work. For instance, shows like The Big Valley and The Virginian would have the regular players be the "passing crowd of the public" for whatever guest stars came around with their drama.
In other words, the "drama kings and queens" come and go.
In this show, there was always some ironic twist to a "cold case" of murder. It might not even be "murder" when it's figured out.
There are lots of "flashbacks", and of course these don't involve the regular players.
The show had a fresh approach that one doesn't generally see from the usual hacks of the writer's guild.