When Nolan goes to Captain Anderson's office to view his bodycam footage, she tells him to get the door, but it doesn't close completely. When Nolan goes to leave, the door is closed.
When Nolan and Bishop capture the thief in the game room, Nolan takes the thief's backpack off, yet when they leave, neither Nolan or Bishop are carrying it.
When Nolan shoots the suspect in the upstairs bedroom, a gold inner barrel can be seen in his handgun. This shows that his service weapon is actually an airsoft replica.
When an officer uses deadly force on the job, they are not automatically arrested; instead, the situation is thoroughly investigated to determine if the use of force was justified based on the circumstances, and if not, then legal action may be taken, including arrest, depending on the findings of the investigation.
When Nolan fires on the suspect inside the house, the barrel of Nolan's gun is clearly visible, revealed to be indeed an Airsoft gun, powered by propane to simulate the cycling of a real firearm. More than likely this was used to eliminate the sound possibly damaging the hearing of the actors inside an enclosed space, as well as eliminate the dangers of a blank round being fired in such close proximity to another person.
In an operation such as the drug buy, the police would not just cover the front of the building. They would cover all exits so that the suspects could not escape as took place.