Question: Throughout the film, there are segues which feature blood seeping through what looks like some kind of fabric. Does that represent anything, and if so, what?
Chosen answer: It represents Al Pacino's character planting evidence on men he knew were guilty. He was planting the victim's blood on their clothes so the evidence would be stronger against them.
In addition, there is a repeated scene where someone (Dormer) is wiping something on or off a fabric.
Question: At the end, Maura Tierney is lying on Al Pacino's bed, having a nap/sleep. Are we then to presume they had sex before Pacino went to the airport to catch his plane back to LA?
Answer: OMG, even my 7-year old daughter realised that the scene was made for the exact opposite reason. Dormer and Tierney talked "all night" and Tierney was sleepy. Dormer and Tierney had a genuine (if short-lived) friendship. Her sleeping on his bed only referred to their trust in one another. His bed had no metaphorical meaning. In fact, it was Ellie who developed a strong crush on Dormer. A crush that interfered with her objectivity as a policewoman.
Chosen answer: Since no answer is given in the film, the audience must make their own assumptions.
Answer: Plot device to make Ellie look like a super sleuth remembering Dormer even carries a backup. When Hap and Dugger were comparing guns Hap says he and Dormer both carry S&W .45s. This makes the 9mm casing Ellie found a complete mystery to everyone else. So why the switch? Dormer's primary might be empty, but this is the first time Dormer shoots and all the characters act like there are only two shots fired in the fog, so for it to be empty he would have to be terribly sloppy. If he's so bad he forgot to load his gun it's equally likely he left the safety on. Maybe Dormer is just so used to being a dirty cop he instinctively uses the backup whenever possible to create an alibi. Ultimately, there is no explanation for this in the film, and if blink you don't even see the switch and are very confused when the 9mm casing shows up in the first place, if Nightmute carries.40, and Dormer .45, then 9mm has no place at all.
In the Netflix version with subtitles, when Dormer fires his primary weapon, the subtitle says "gun clicks." Dormer briefly looks at his gun and then pulls his secondary weapon. Nolan may have intended this to be ambiguous so the viewer doesn't know whether it was an accident or intentional (Nolan would never leave a "mistake" in the final edit - in fact, in interviews, he said he watched the movie at least a hundred times while editing), but the subtitles seem to put this debate to rest.