Help with similar movie

I vaguely remember seeing a b&w movie from roughly the same period, which had a few common elements.
The murderer uses some sort of gas to kill his first victim while she is asleep/ unconscious in her room. During this time he is hiding in a secret cellar and wears a gas mask, presumably to protect himself form inhaling.
Just like the killer in Gaslight, the protagonist then moves on to the victim's sister/friend, can't remember if it was for material gain or just to eliminate a suspicious relative of the victim.
The plan almost works, but when he's trying the same trick again, the second victim is rescued just in time and he remains locked in the cellar by a massive piece of furniture who is unintentionally moved, thus blocking the cellar's secret door.

Sorry about being so vague, but I was less than 10 years old and it's been almost 30 years...

Any idea what movie might have been?