[78-L] ^Film query off topic

[Julian Vein]

Around 1947-8 I saw a creepy film that took place in a mansion involving 
a man wearing a rubber mask hiding in secret passages, peeping through 
eye-holes in portraits and attaching electric cables to candelabras and 
electrocuting those unfortunates who touched them. I thought it was 
called "The Unknown" (!946)--part of the "I Love A Mystery" series, but 
I've just seen that and it's not the one, although that also involves 
secret passages.

Any ideas?

      Julian Vein