Who is Leslie Murdock from The High Window and what is their importance?

Leslie Murdock is Mrs. Murdock's son. He lives in his mother's oppulent home, and he s married to Linda Murdock. Leslie is described as effeminate and weak, but in the end, we learn that he is, in fact, the murderer of Louis Vannier. Murdock gambles heavily and is in debt to Alex Morny.