I found Detective Cameron (Joseph Cotten) to be most interesting. His
character is unwilling to give up on the long dead murder case,
despite the unlikliness of solving it and direct orders to do so.
Like a cat's whiskers (or any good detective), his curiosity is
perked up by seeing a familiar face and sensing strange behavior and
something out of place.
The scene where Elizabeth, the housekeeper, first lets Detective
Cameron in then eventually lets him out and later denies he was ever
there. She is told twice to act in "her mistress's best
interest" and she does just that, then eventually says wryly,
"(now) I understand exactly what is going on".