 You'll notice there isn't another photograph of Tom Sanford left on that wall. Okay. So assuming the killer took these away because they might identify Barney as Tom Sanford... Link him with Mavis Gale? Yes. Yet the killer went to the trouble of drawing red question marks over the other photographs of Mavis Gale. To deliberately draw attention to her. Why? Mavis Gale would have been involved anyway to a certain extent. After all, she is the beneficiary of Slade's insurance policy. Sure, sure. But suppose the killer wasn't aware of that.