Naturally, much is made of the relationship between Neff and Phyllis Dietrichson (Barbara Stanwyck), but the relationship between Keyes and Neff is equally interesting, if only because it marks an early version of bromance. Also, their chaste relationship forms an interesting parallel to one between Dietrichson and Neff. While Dietrichson is betraying Neff, Neff is betraying Keyes. As played by Robinson, Keyes exudes a gruff and completely endearing morality. Perhaps the worst aspect of the morass Neff finds himself in is it necessitates misleading his friend.
"I didn't get the money, and I didn't get the girl."
"Suddenly it came over me that everything would go wrong. It sounds crazy, Keyes, but it's true, so help me. I couldn't hear my own footsteps. It was the walk of a dead man. "
I like how Wilder uses physical groupings to highlight certain tensions. Here Walter Neff is visually trapped within the frame between Keyes and the one witness to Neff's crime.
I also love this sequence of shots, in which Dietrichson is trapped behind the door to Neff's apartment. The depth of field in these frames creates a really beautiful effect that seems to reduce the characters to one plane, while physically separating them. They seem to exist in a fragile balance on the screen. Once again, Neff is trapped between two major forces--the total morality embodied by Keyes, and the temptation embodied by Phyllis Dietrichson.
And my favorite scene.
"No, I never loved you Walter--not you or anybody else. I'm rotten to the heart. I used you, just as you said. That's all you ever meant to me. Until a minute ago, when I couldn't fire that second shot."