During the opening locker room scene, Officer Taylor states "this is the department issue sidearm; Glock 19." The gun he holds up to the camera, however, is clearly stamped "22" and ".40," indicating that it is not a 9mm Glock 19 but instead a .40S&W Glock 22.
When Van Hauser and Sook come to release Taylor and Zavala to go back on patrol, after he goes under the tape he takes his cigar out of his mouth he spits. This is an official crime scene, that's whats called "leaving your own evidence on the crime scene". Professional police officers don't spit or leave any of their bodily functions on the crime scene. That confuses the case. They would also not allow an officer on duty to smoke s cigar let alone inside a crime scene.
When Officer Taylor and Officer Zavala are pursing a gray Ram pickup truck, Taylor tells dispatch that the license plate is "4Boy1732". However, when Officer Zavala is putting handcuffs on the suspect, the license plate reads M4BE195.
As Taylor and Zavala drive towards the house they set out to search, there is no passenger cage in the vehicle they are driving. However as they exit the vehicle, another shot shows their vehicle to be a marked Police Interceptor with a passenger cage installed.
When they are driving and spot the fire they help with the dispatcher asks for a location which they identify at 1002 6th St. During the scene following at the house that they find the human trafficking ring, they ask for backup which the dispatcher calls for additional vehicles to respond to 1002 6th St. A minute earlier, they had identified this house as "9318 53 Street".
While Mike and Brian are driving around at night prior to finding Van Hauser stabbed in the eye, they are driving a Crown Victoria with gray vinyl / leather seats, as soon as they pull up to the crime scene, Brian gets out of the Crown Vic and the seat he was sitting in is the black and gray cloth seats.
When the 2 officers are performing the "Welfare Check" on the house, right as they are about to kick in the door the reflection of the window to the left of them shows a blue tent and several crew members in the back behind the scene.
During the locker room scene, Officer Taylor states the standard issue sidearm for the LAPD is a Glock 19. This is incorrect, as the standard issue sidearm is a Glock 17 (9mm) issued to recruits in the police academy which they must carry for their one (1) year probationary period. After successfully completing their probation period, officers can then purchase and carry a firearm of their choice off the department's "Approved for Carry" list, which includes the Glock 19.
During the pursuit in the opening of the film, the officers pass by a homeless man on the ground as well as a yellow truck on its side with a potentially hurt passenger trying to exit the vehicle. Police procedure requires an officer to stop and render aid, even in a pursuit. It does not appear any other police unit was following the officers (a second unit could of stopped to render aid), so they would have been required to end the pursuit and help the injured.
Throughout the entire movie while "Brian" and "Mike" are inside their patrol vehicle, where the center "cage" or "divider" mounts to the vehicle above each persons seat belt, the plastic cap that normally covers the mounting bolt is sometimes there and other times it's not. The bolt is gold in color and it seems to happen to "Brian's" side more often. Sometimes the gray cap is there covering the tops of the seat belts, other times the gold bolt is visible.
When showing the burned up stolen vehicle the officer states they found two types of shell casings, 9mm and 45. However, the brass they find is 7.62x39mm, 9mm, and .45 ACP, correlating to the three calibers of weapons used in the drive by scene.
The goof item below may give away important plot points.
In the very last scene of the movie, after the funeral, the driver's side sun-visor goes up and down several times on its own. In one shot of it down, there is clearly some audio equipment visible and in the next shot it is gone.