Alfred Hitchcock Presents: Kill with Kindness (1956)

Katherine Oldham sees a homeless man in the park, feeding the pigeons. He looks perfect. Her brother, Fitzhugh, his mind either on a bird or his butterfly collection, absent-mindedly agrees. She brings the old man inside and feeds him some stew. The man dimly suspects something is wrong when the eccentric brother blurts out something about killing and substitutes and insurance. But his benefactors seem so nice. And they even give him a new suit of clothes--Fitzhugh's clothes. And they let him spend the night. He may have spent his last night on a park bench--or anywhere else.