Ellie Burr: A good cop can't sleep because he's missing a piece of the puzzle. And a bad cop can't sleep because his conscience won't let him.
Will Dormer: This guy crossed the line and didn't even blink.
Will Dormer: You shouldn't knock misdemeanors.
Ellie Burr: Oh, but it's small stuff. It gets so boring.
Will Dormer: It's all about small stuff. You know, small lies, small mistakes. People give themselves away, same in misdemeanors as they do on murder cases. It's just human nature. Aren't you gonna write that down?
Rachel Clement: I can't judge. There are two kinds of people in Alaska: those who were born here and those who come here to escape something. I wasn't born here.
Hap Eckhart: But you're clean, Will.
Will Dormer: I'm a good cop, yeah. But there's always something they could use to get at your credibility.
Walter Finch: You have no evidence I killed Kay. You only know because I told you what I saw.
Walter Finch: You're a good man. I know that. Even if you've forgotten it.
Will Dormer: We better find out where this came from.
Ellie Burr: I tried. Mrs. Connell doesn't know, her friends didn't know.
Will Dormer: Have you tried the jewelry stores? Small things, remember? The second you're about to dismiss something, think about it. Look at it again.
Ellie Burr: Want me to write that down?
Will Dormer: No, I'll remember it.
Walter Finch: You and I share a secret. We know how easy it is to kill someone. That ultimate taboo. It doesn't exist outside our own minds.
Ellie Burr: So, I'm gonna just take you guys over to the lodge, and.
Will Dormer: Just take us to the station.
Ellie Burr: Right. We need to get started. Most homicides are solved by work done in the first 72 hours.
Will Dormer: Well, it's 48 hours. We're a day behind. But who's counting?
Walter Finch: You forgot the wild card, Will.
Francis: This his blood?
Ellie Burr: Ketchup maybe. Was he eating a hot dog?
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.