Double Indemnity as "Black Film"

Double Indemnity is considered film noir because of a variety of elements present that scream, "black film." The first aspect you might notice is that the film occurs at night in a very foggy urban environment, which we shortly find out is Los Angeles. Almost as soon as the first scene opens there is car speeding recklessly, immediately creating a sense of danger and uncertainty. Then, throughout the rest of the film, there are excellent examples of the visual conventions that make it considered a "black film," much of which were derived from German expressionism. These include dark interiors, heavy shadow, high contrast, bars or slashed of light (often created by often created by the shadow of slatted blinds), mirrors, lots of fog and rain, odd angles and disorienting compositions, and staircases, just to name a few. Furthermore, the shadows of the slatted blinds created a "prison" effect and always fell on the characters who had done wrong or were going to do wrong at some point (foreshadowing or nah?). For example, when Phyllis visits Walter's house for the first time, they sit on the couch and, almost immediately, a shadow of blinds falls on both characters, signifying that they will both do something bad at some point.
Another aspect of Double Indemnity that makes it film noir is the flashback structure, which emphasizes the noir theme of fate. The dialogue summarized the story from the start when Walter says, "I killed Deitrichson...Yes I killed him. I killed him for money, and for a woman, I didn't get the money, and I didn't get the woman. Pretty, isn't it?" From there, we see that the film begins near the end of the murder story and tells the story through voice-over and flashback. By having Walter narrate through an office machine, the director made the voice-over diegetic. An example of fate as a theme of the film is near the climax when Walter says, "I remembered what you had told me, Keyes, about that trolley-car ride, and how there was no getting off until the end of the line, where the cemetery was." The line, "straight down the line" is a metaphor for fate.
Overall, these elements of film noir, or "black film" gives the effect of a dark and depressing murder mystery story. The story really has no happy ending and no certain hero. In the end, the insurance investigator, Barton Keys, prompted by Mr. Deitrichson's daughter Lola, uncovers the truth of his death through clues left by Walter and Phyllis. Also, as Walter admits at the very beginning, his motivation for his actions did not go through, He "didn't get the money" that he had hoped for and he "didn't get the woman" (Phyllis) that he fell in love with (and rather quickly, at that).