This is one I've been tracking down for years. It's in the mid '70s and I was maybe 15 and watching what I thought was a made-for-TV movie. It was a mystery with a detective and a girl sneaks into the house of a suspect one dark night and notices that the moulding along the top of the room didn't match the other 3 walls and realized there was a false wall built in.
They broke through it to find what they thought was hidden evidence (or something hiding behind it), with axes or hammers. But behind the wall they found grandma (?), mummified, wrapped in plastic and apparently buried there decades ago. Actually sitting in a rocking chair, sideways. ("She wanted to be buried here in her own home.") It was a horrific scene and I remember it not being so much a clue as just back story for the eventual suspect. The rest of the film was more a straight forward procedural (I think!). I'm not even sure I watched it to the end so I never got closure that way either!
Certainly influenced by Argento (Deep Red) and Psycho, not even sure if it was an episode of Night Stalker (although I've looked through synopses of those and never discovered a mention of this). I have the feeling it is American rather than an Italian giallo dubbed for TV play.
Does this ring a bell for anyone?
Thanks in advance,