In double indemnity the role of the femme fatale is played by Phyllis. She talks about her husband to Walter "I feel as if he was watching me. Not that he cares, not anymore. But he keeps me on a leash so tight I can't breathe." The femme fatale character represents the lack of fulfilment and of status women can feel in a conventional marriage.
Phyllis and her husband also do not have a child of there own, just a child from his previous marriage showing his lack of interest in his wife. Also when Walter enters the house for the first time he notices the pictures. There were no pictures of Phyllis just of the father and daughter.
Although Walter was the one who actually committed the murder the audience feel sympathy towards him as he was being manipulated by Phyllis and he seems weak and helpless. He can't seem to control his emotions but is controlled by his environment. Dramatic irony in the film allows the audience to give more attention to the rest of the storyline as they are not wondering who the murder is as Walter has already confessed.
The motives are typical of film noir. Walter killed the husband for love, money and because he had fallen into Phyllis's trap. It showed his insecurity that he was willing to commit the murder when he had only met Phyllis a few times. Phyllis's reasons were money and desire of independence. When...