I'm not sure it was a novella, or even a short story. It might have been a "treatment". In some of the articles it's referred to as a short story, but with never an attribution. Given his other writing (e.g., for Lux Radio Theater), I'm inclined to think it was just something he wrote and was never published. You can get a bit of insight from the L.A. Times obituary (which, tellingly, mostly refers to an obituary he wrote for himself).
Sanford (Sandy) Barnett, whose writing talents ranged from adapting films and plays for "The Lux Radio Theatre" to composing stories that won Academy Awards and lastly to speeches and press releases for the Los Angeles Police Department, is dead, the department announced Friday.