Horror movie, I think

I was a young boy when I saw this. So I'm thinking it was in the 70s when I saw it.

All I remember is a kid playing the piano while the kid's father kills his wife. I think the wife's body is kept hidden away during the movie.

That's about all I got, really. From what I can remember it happens during the Christmas holiday. But I could be wrong about that. And I don't think you see the father killing his wife outright. You see the shadow of the action.

Is the movie in color or black and white?

I'm pretty sure it's color

Here's something else. The more I think about it the more I remember the stabbing as a shadow cast on a wall.

Omen?

!
Oops never mind, just read that it was from 70's..

Is the bit you describe at the start? Does the boy grow up to be a killer?

That's the thing. I keep thinking it's at the beginning of the movie. Then later in the movie you see the woman all rotted and still sitting in a chair.

I started going through all the made for tv movies in the 70s and 80s to see if anything rings a bell. I've come up empty though.

This has had me puzzled for a long time. Sometimes I think it's just something I've made up in my mind.

Welp. I've done every bit of searching I could. If anyone has any leads let me know.


Or do you all think I've made it up in my head somehow?

Don't read the following if you have not seen Deep Red:

Are you getting mixed up slightly with the genders, in Dario Argento's Deep Red/Profondo Rosso there is a similar murder sequence during Christmas, a shadow on the wall of the killer with a knife, and a body/skeleton of a man behind a wall.

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Some of it looks familiar. I need to watch the whole thing to be sure.
But, thank you so much for the reply.