What Became of Jack and Jill (1972)
In order to collect inheritance money, a slacker tries to induce a heart attack in his invalid grandmother by convincing her that shes become the target of youth supremacists who want to enact a genocide on the elderly
Night Must Fall (1964)
A psychotic killer gets in the good graces of his aging invalid employer, and worms his way into the affection of her beautiful daughter, with unpleasant results for all