The Killing Time (1987)

To commit the perfect murder, you need planning, guts, and luck. Practically nobody has luck.

After a psychopath murders a man who was on his way to a job as a deputy sheriff in a small California town, he assumes the deputy's identity and arrives in town to start his new 'job'. What he doesn't know is that the recently appointed sheriff and his mistress are plotting to murder her evil husband—and blame it on the new deputy.