Hitch Hike to Hell (1977)

Howard Martin is a mild-mannered young man who lives with his widowed mother and has a job driving a red van for a commercial dry cleaning service. He is also a homicidal psychopath and a Mama's boy whose sister, Judy, ran away from home and broke his mother's heart. While he delivers his customers' dry cleaning to them, he picks up young female runaways who are hitchhiking in the red van, then asks them if they ran away from their mothers. If they say "Yes", he then rapes them and kills them for their "transgressions." As the bodies start to pile up, the police finally start to investigate.