After Kersey self-treats his shoulder wound, he doesn't show any signs of being wounded.
When the doctor arrives at the liquor store, he's wearing gloves. He walks inside and up to the bead curtain, we cut to a view from inside the curtain as he walks through it, and his gloves have vanished.
During the shoot out in the back room of the bar, Bruce Willis switches hands left to right. The story makes emphasis of his left hand shooting and injury as a result.
Paul stuffs a wadded rag into Joe's mouth. But it changes to hanging down, then wadded again.
Paul moves the three cans of brake fluid from the floor next to Joe's head and places them on his body. They briefly reappear next to his head again before disappearing.
Murder case tags on bulletin note type of weapon. Some list knife, those with firearms list caliber." .45 caliber" is listed in several cases as "45mm." Caliber is diameter, and .45 is .45 of an inch, not 45 mm. "45mm" would be a bullet almost two inches wide.
The detectives first appear for the shootings in Evanston Il. but later in the movie, the same investigators show up for Chicago shootings, and their office is in Chicago. Obviously one city or another is out of their jurisdiction.
When Paul fires his gun while lying on the ground, he is holding the gun in his left hand only, and sustains an injury to that hand from the slide pinching the skin between his thumb and index finger. This injury occurs frequently to an untrained shooter, but not as shown. That injury occurs when a novice shoots with both hands gripping the gun, and forgetting to have both thumbs on the same side of the gun. In that case, the injury is to the top (non gripping) hand, not the shooting hand. Paul was not using a two hand grip, and even if he had, the injury would have been to his right hand for a left hand shooter.
When he has the car jacked up over the killer, to drop the car, he shakes the chain. With the weight sitting on the jack, he would have needed to pull pretty hard to get the jack to fall out from under the car.
After the funeral, and the Lucy's father shoots at the poachers, he shows no kick back when shooting.
When the two detectives describe The Grim Reaper as a left-handed, white man with a hoodie, their chief states that there are a million suspects. However, if the population of Chicago is 2.7 million as of 2017, then the number of people who would be left-handed, white, male and of the likely age range would be closer to about 40-50 thousand.
In the opening, it shows an overhead shot of a squad car with light and siren weaving through traffic to get the injured officer to the emergency room. This is improbable because driving laws require cars are to pull to the side when drivers see and hear the lights and sirens.
To the gentleman commenting about the wound to the doctor's left hand and saying that this ONLY happens when shooting two-handed and crossing thumbs. It can (and ha happened to me) happen when shooting one-handed and having a grip that's too high. First time shooting a semi was on a Ruger Mark III 22/45 and the pistol bit me on the way back INTO the upper..
During the bar gun fight the bad guys Beretta locks back due to being empty although it was still "clicking". in the scene you can see the slide go forward and he resumes pulling an empty trigger. When the scene cuts back the slide is open again with no way for him to have done so.
Initially when Paul places Jordan under the stairs, from the outside there is clearly an air vent behind her head. When Paul closes the door on her, the next shot from within shows no air vent.
Kersey doesn't wear gloves and leaves fingerprints all over. The cops never dust for prints.
When Kersey puts the brake fluid cans on Joe's chest, they clink together and are obviously empty.
When Bruce Willis is in the nightclub and looks at his cell phone, the messages are reversed. The owner of the phone's messages should be on the right and the sender's on the left, not the other way around.
The climax at the end of the film involves Paul using guns he has purchased legitimately from a gun store against the thugs that break into his house, but one of the guns he is shown using is clearly a machine gun. You cannot legally own/purchase a machine gun in any gun store in the state of Illinois. One could argue that he purchased/acquired the gun on the black market, but if this was the case, he should have been arrested for possession of an illegal weapon when the police arrived at his home.
Currently, these states allow private ownership of machine guns: AL, AR, AK, AZ, CO, CT, FL, GA, ID, IN, KY, LA, MA, ME, MD, MS, MT, ND, NE, NV, NH, NM, NC, OH, OK, OR, PA, SC, SD, TN, TX, UT, VA, VT, WA, WV, WI, And WY; provided all the correct paperwork are filled out and then given approval by the BATF.