After Will and Walter's conversation on the ferry, the officer who got shot in the leg earlier by Walter is shown walking normally at the police station. Later he's shown limping and using crutches.
Photo of Walter that Will picks up from Walter's house remains dry despite the fact that Will fell into the water when chasing across the logs. There are no signs of the fact that it got wet when it is next shown.
While they are meeting on the ferry, Dormer's position in relation to Finch changes repeatedly from shot to shot. Dormer quickly alternates between facing Finch and facing away from him.
When Ellie Burr asks Dormer to sign the report and Dormer tells her to be sure of all of her facts, he walks out of shot having taken his glasses off. In the next brief shot of him passing by so we can see Ellie's reaction, his glasses are back on his face.
The dead dog in the alley has been dead for quite some time. When
Dormer uses the gun, then digs out the spent bullet the dog's blood and flesh seem very bright and fresh. The blood would have coagulated and the buzzing flies indicate that the flesh had begun to deteriorate, thus giving off an odor.
Dormer, a seasoned police detective who demonstrates in the story that he understands the properties of blood, including DNA and proteins, chooses to use hot water to clean the blood off his clothes (you can see the hot water tap is wide open and the cold tap is closed in the sink in his hotel room). Hot water binds blood to clothes and makes a permanent stain. Cold water removes blood.
The actual town of Nightmute, Alaska is several hundred miles south of the Arctic Circle. Therefore it would be impossible to have 24hr daylight.
In the phone book that Dormer browses in search of Finch's address, the name of the town is spelled 'Umkumuit' instead of correct 'Umkumiut'.
The information regarding Glock pistols is incorrect. The slide, while it is steel, does not have a blued finish. The finish is called Tenifer, and is proprietary to Glock. The Tenifer makes the slide essentially rust proof. The only parts that may have a tendency to rust are the sights which have a different finish. Gun enthusiasts often refer to the Glock as "dishwasher safe".
Glocks have more metal than just a barrel and firing pin. Only the lower receiver and magazine is plastic. The entire slide assembly and all internal mechanicals are metal.
At the beginning, when Ellie Burr is telling Dormer how she knows about his past cases, she asks if the scar on his neck is where Ronald Langley cut him during the Leland Street Murders case, but then immediately says that the Leland Street Murders were her case study at the academy. If so, she should have known that that was where he was cut. This could be attributed to the character's nervousness at meeting Dormer.
The comment about Walter's trigger finger position is partially correct. A double barrel shotgun usually has two triggers, one behind the other and one for each barrel. It's reasonable that an open trigger would be visible while firing with the second trigger.
When detective Will Dormer falls into the water then reaches the ladder to get out, then looks at the suspect then turns and walks up the walkway you can clearly see the life jacket under his suit.
Obvious stunt double with a wig as Dormer is chasing Finch immediately prior to the log-chase sequence.
On the ferry, the Pacino character and the Williams character have a long discussion. Outside the window of the ferry the foreshore scenery does not move, yet they are supposed to be sailing somewhere.
The closeup of the so-called blood stains clearly reveals by its transparency that it is red sugar water, and not real blood, which is a different color and is not translucent like fake blood.
When Ellie is giving her report to Dormer, after the shot changes to show Dormer, Ellie's face can be see on the left but her lips aren't moving when she is saying the word "paperwork".
During the foggy chase, an orange extension cord is visible on the ground at Dormer's feet as he is running.
Dormer displays abysmal handling of his service weapon, consistently violating the third of Cooper's four famous gun safety rules ("Keep your finger off the trigger till your sights are on the target."). What's more, the death of his partner is a direct result of Dormer violating the fourth rule ("Identify your target, and what is behind it. Never shoot at anything that you have not positively identified.") Given his age, it is possible that Dormer went to police academy before it was common for law enforcement agencies to require their staff to comply with Cooper's rules (i.e. before around 1985). That the young Burr, who leads the investigation of the incident, would neither mention Dormer's outrageous violations nor try to find out whether he had received updated weapons training is, however, utterly impossible.
In the climatic shootout, Dormer tells Burr that his pistol has seven rounds in its clip. As a police officer, he should have known that pistols hold magazines, not clips.