Precursor to the looming onslaught of slashers

This is a drama/mystery with some horror elements that was originally released as a TV movie on ABC, running the typical 74 minutes (which makes it short 'n' sweet).

As my title blurb says, it was the forerunner to the forthcoming rush of slashers by the early 80s. Sure, it's understandably tamer and more dramatic, but it has a killer in a hooded raincoat with a pitchfork, as shown on the poster, which is reminiscent of the slicker killer with a hook in "I know What You Did Last Summer" (1997).

The flick works up some nice creepy ambiance with the storm, the mystery slayer and the macabre deaths. While Sally Field is fetching, Jill Haworth wins out on the beauty front IMHO.

Forty minutes into the story I had a theory about the identity of the murderer, but changed my mind five minutes later and was right. See if you can figure it out.