Other mistake: When Jack Vincennes goes to the hotel to stop actor Matt Reynolds from sleeping with the DA, he finds Matt's dead body on the floor with his throat slit. In the closeup of Matt's face, you can clearly see the living actor's pulse in the left side of his throat. (01:14:20)
Other mistake: When Exley talks to Vincennes about Rolo Tomassi, Guy Pearce's Australian accent accidentally slips when he says, "I just wanna solve this thing." (01:26:20)
Other mistake: In the fight scene, Exley hits all the soft boxes, but he rams his head into his hands so he doesn't hit the hard file cabinet. (01:48:50)
Chosen answer: A 12g shotgun blast at that range would cause an incredibly bloody death, especially as there is a good chance it hit the man in the face. Exley has killed a person in the line of duty before this, but not in such a spectacular way. And while he may not have meant to kill him he chose to shoot over letting the man escape.
Grumpy Scot