While Kathy and her dad are trying to find their way to the nanny, Kathy spots a police car and suggests they ask the police for help. Looking out through the front window of the car, we see a deserted roadside with only the police car. Looking out the rear window a moment later, we see the police car in a row of other cars.
Kathy is casually shot by a gang member when she wants to get the ice cream cone she ordered. She is shot holding the ice cream cone. When her father goes up to her when she's dead on the ground, the ice cream cone is nowhere near her.
When the patrol car turns around at the station before the final assault the two officers are clearly seen wearing their uniform hats inside the car. Before and after that scene the officers are shown inside the patrol car with no hats on.
When Bishop is hammering in the station has moved sign in front of the station, there are two bullet holes on each side of the front door on the white concrete. Later in the film he dodges bullets when he goes out of the front door to check on the Sergeant after Julie thinks the Sergeant fell down. Bishop dodges the bullets at night when he tries to check on the Sergeant. The two holes are created in that scene.
The silenced revolver that Wells uses would not be silenced. On the vast majority of revolvers have a gap between the cylinder and the barrel, through which some gas can escape, rendering the silencer ineffective.
When Wells hot wires the car and speeds away, the director shows the audience a long insert of a car rapidly traveling a dirt road. The car is at least two blocks away before the gang member in the back seat shoots Wells with a silenced rifle. Yet Wilson, Bishop, and Leigh clearly see and hear the killing but rationalize the sound as perhaps a window breaking.
In the infamous "Ice Cream Truck" scene, you can see a box of Skittles on top of the freezer in the truck. This film was released in 1976, probably shot in 1975. Skittles didn't become available in the United States until 1979, and then only as an import. It didn't become a domestic product until 1982.
When Leigh, and moments later Wilson and Bishop, walk through the basement to the stairs to leave, they walk without having to avoid all the bodies that were there a few minutes ago. It's obvious a little bit of time has passed between the explosion in the hallway and the cops/medical personnel arriving on the scene. The bodies have very likely already been removed, this clearing the hallway floor.