I think the film you are writing about is Without Warning (
http://imdb.com/title/tt0081764/) which I remember all these years later. A real stinker but with a B-movie dream cast; Oscar winners Jack Palance and Martin Landau along with B regulars
Neville Brand, Cameron Mitchell, Darby Hinton, Larry Storch, a slumming Ralph Meeker (for crying out loud he was in Kiss Me Deadly, Paths of Glory and the Naked Spur) and a very young David Caruso.