Maybe Jack Webb was not such an original thinker
I've always heard that Jack Webb was working on a film where Marty Wynn was the technical advisor and that the film was a traditional Hollywood film noir. Wynn expressed his frustration that Hollywood never made realistic films and from that Webb got the idea for Dragnet.
Well, this is that film and it's hardly a typical film noir of the 1940's, like The Big Sleep or Murder My Sweet. Instead it's the original police procedural and a clear blueprint for Dragnet, right down to the "This Is the City" type opening, (which doesn't use that phrase), the names being changed to protect the innocent, the terse dialog, the restrained acting style, etc. Webb is in this but none of those things is his idea. He's just an actor here.
I give him credit for recognizing something that was unique and perfecting it, but it's clear from this movie that what became Dragnet was hardly his idea to begin with.