After the little girl is shot, the father chases the suspect. The car chase clearly starts during the light of day and continues into late dusk. A two hour chase in a populated city wouldn't go unnoticed by police.
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.
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.
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.
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.
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.