Who was the blackmailer?

No actually I was thinking of the banker, who put the house up for auction, and who had come over to talk to her husband. He reminded me of George Sanders, (but, I knew that's not who it was), he looked a little menacing. My question about Gene Lockhart was, if he was Jewish, because he looked as if he was wearing a yarmulke on his head. Wasn't his character a druggist, since it was his store that she broke into and took the arsenic? As for Ms. Jones' performance. I thought it was convincing enough, since the very first performance I had seen her in was "The Song of Bernadette", quite a change in character.