Continuity mistake: When Dormer and Finch meet up after the interrogation, Dormer slams Fince against a metal support beam and the position of his hands of Finch change from being pressed against Finch's left cheek to being pressed against his neck/shoulder area as the camera angle changes. Happens about 3 times during scene.
Continuity mistake: When Robin Williams is being questioned by the police for the first time, one of the cops is talking to him. Very soon afterward the cop leaves the room and is walking away. We see the cop in the distance in another room, yet we hear the cop talking to Robin Williams again as Al Pacino shuts the door. Almost immediately, the camera angle changes to the cop as he finishes talking. He is standing in front of Robin Williams again.
Continuity mistake: When Dormer first goes to Finch's apartment, you see him taking out his gun and holding it in his right hand as he starts walking down the hallway. Camera angle changes and the gun is no longer in his hand. Camera angle changes again and the gun is back in his hand.
Continuity mistake: When Al Pacino runs along the boardwalk towards the floating logs, following Robin Williams, in the shots showing him from behind he is running with his arms spread at a considerable angle, while in the shots showing him from the front, he is keeping his arms into his body.
Factual error: Al Pacino is the subject of an internal affairs inquiry in Los Angeles. It's unlikely a police officer under investigation in L.A. would be sent to Alaska to work on a murder case. Police officers under investigation are routinely given desk assignments until officially cleared and allowed to return to active duty.
Continuity mistake: During the final fight, Pacino & Williams shoot it out in a small boathouse. Williams is shot and rolls into the water (dropping about 2 foot before splashing in). Pacino walks out of the house and meets the female officer. The camera pulls back to show the boat house on stilts about 20 feet out of the water.