This is a movie I saw on TV in c.1981-86 in the UK. I think it was American but I can't be sure whether it had subtitles and was just set in America, unknown cast (to me anyway).
The patriarch of an East European immigrant family has accepted custody of a relative. The relative looks to be late teens to early twenties and has been in some sort of trouble, shaming the family. I have the feeling he'd been passed around a while.
When the youth arrives the old man lays down the law: the youth must behave and if the old man hears that he has done anything "wrong" he'll see that that is the "end" of him.
The youth appears to toe the line at first, but we see a scene where he enters a couples' home at night while they are in bed. He somehow renders the husband unconscious after assuring him that he will wake up, then he does something to the wife (possibly rape but without noise, drugged perhaps).
The old man becomes suspicious of the youth's comings and goings, and rumours about this incident. He warns him again more sternly.
Feeling sad and misunderstood, the youth befriends an older local woman who is also depressed. The woman later commits suicide for unrelated reasons.
On hearing about the suicide the old man immediately accuses the youth of killing her, which he denies. He is innocent... this time.
As good as his word, and against his devout nature, the old man is obliged to "end" the youth. Afterward the family are sorry but relieved.
The film had a very dark, sombre and disturbing vibe. It seemed to have been shot inexpensively, could have been art house, maybe black and white, but the acting was decent.
I remember being uncertain whether the youth was or wasn't a vampire or just had some hereditary syndrome that could be the root of the mythology. I think you weren't meant to be sure.
Either way I think that is the fantasy or sci-fi element in the story.
Can anyone identify this?