When Hatch is in the rear of the car with the two FBI agents he shoots them both in the back of the head from point blank range. The following day when the bodies are discovered neither show any signs of an exit wound, which would be virtually impossible from such a close range with such a powerful handgun.
When the office chair is hurled from the window, the bird's-eye view shows the ground to be dry. Seconds later, when the chair lands on the car, the ground is wet.
Also, when the chair hits the car, the windscreen shatters. In the next shot, when the chair is bouncing off the car roof, the windscreen is undamaged.
Detroit PD's tactical unit is known as SRT (Special Response Team), not "SWAT" as shown in the movie.
When speaking to Cutler, Kim Byers makes a reference to a 5150 psychiatric hold. 5150 refers to California Welfare & Institutions Code section 5150. There is no such code or section in Michigan law
During the opening credits, spent shell casings can be seen loaded into the magazine. The spent shell casings are identified by the indentation of the primer from the firing pin.
During the raid in LA, Cutler tells Slater Harrington to drop the AK.
Later, Cutler sweeps a cube farm with his rifle shortly before his first encounter with Hatch. In both instances the Eotech sight is mounted backwards (battery compartment towards stock, not muzzle).
The LAPD use the Federal Signal Arjent light-bar rather than the light-bar shown in Los Angeles hostage situation scene.
During the telephone conversations when Hatch is firing the .50 cal rifle, every shot he fires gives no recoil, not even a rustle of fabric on his shirt. The recoil of a such a weapon is widely documented and even with recoil dampeners should still be visible.
In several shots, the Eotech holographic sight on Cutler's rifle is mounted backward. Eotech sights are mounted with the taller portion housing the glass lenses toward the rear of the rifle.
When Sgt Cutler and the team are in the bar and playing the boxing game, after Kellog takes his turn and Cutler takes Kellogs gun he takes the clip out and he cycles the slide, when the bullet hits the floor you can hear that the cartridge was empty (no bullet or powder).
When Walter Hatch shoots the FBI agents, he is in the back of a car, shooting both agents in the back of their heads. Next day, when the police arrives at the crime scene, it clearly shows that at least the co-driver is shot through the forehead.
In the opening credit sequence, a clip is loaded with spent shells - they've already been used.
The Detroit Police cars' liveries in the movie are old ones from 2003/2004. The liveries in 2010/2011 were white with blue stripes and red letters, as opposed to the black with gold stripes.