I saw this film on TV in the UK, probably in the late 1960s or early 1970s
I beleive it was in black-and-white, but can't be sure as it was a B/W TV!
No idea of the title
No idea of any of the cast, or whether they were famous/big stars etc
I'm **guessing** it would have been from late 1930s or 1940s
I think it was set in England or U.S.

Here's what I can remember of the plot:
A person (a woman I think) is found dead in a room locked from the inside.
Later the murderer commits another murder with the same method, but we see how its done -
the murderer gives the victim a glass of drugged milk, and when this has taken effect,
locks and seals the door to the room with tape (to delay discovery ?), and turns
on the gas fire in the room, unlit, to cause asphyxiation/poisoning of the unconscious victim.
Murderer then hides in a chamber under the floor and waits for victim to be discovered.

At the end of the movie, the victim has been discovered, but the murderer cannot leave
his hiding place as some heavy item of furniture (wardrobe ?) has been moved to on top of the
trapdoor/hatch in the floor.


Hope someone can help !

Bonzodog: Although the plot and description are not familiar to me, I can see why you would want to track it down. It appears to be a really eerie and curious flick. Have you tried doing a search of Alfred Hitchcock's early efforts? While reading your description of the film his name immediately popped into my head.