Continuity mistake: When Brian gives Mia a Snapple to drink, she takes a drink of it. Her hand position and the label of the bottle change from the shot from Mia's front and the side shot of them both as she is taking a sip.
Continuity mistake: When Brian drives up to the street racers meeting in the alley, there is a pipe of some sort hanging from his engine. When he picks Toretto up, it's no longer there. (00:10:00 - 00:24:00)
Continuity mistake: At the end of the film when Dom flips it the Supra has a full roll cage, but in every other scene it's only a yellow half cage.
Continuity mistake: When Dom and Brian are back at Dom's place right before Jesse gets shot, there are blood stains on Dom's shirt. The stains seem to change during the shots between Dom and Brian.
Continuity mistake: Just as we see Dom's Civic get shot, there is a shot of the track driving along. In this shot, Vince is not on the truck. (01:22:10)
Continuity mistake: At the end, as the crew go for the last hijacking, we see all the cars driving over a bridge. However, the railings that are on the side of the bridge are not visible when we see the inside of Leon's car. (01:17:40)
Continuity mistake: When Tran and Dom are arguing at Race Wars, the distance between them changes instantly. (01:11:10)
Continuity mistake: When Dom walks out of the parking garage, he puts his hand to his mouth. Camera cuts and his hand is down by his side. (00:23:30)
Continuity mistake: In the first hijacking, the window is pulled out and the rubber seal hangs from the lorry. Camera cuts to the next harpoon and the seal has gone. (00:01:30)
Continuity mistake: When Brian is calling for the air ambulance, he switches which ear his cell phone is on between shots. (01:24:05)
Continuity mistake: When the first street race takes place with the four cars, it is evident that the race takes place along a straight stretch of road. However, when the race finishes, everyone who was at the start line just a minute ago has magically appeared at the finish line, miles down the road.
Answer: There are two ideas of why the police did not come around. Firstly they might have found out after the car chase that Brian was an undercover cop so it would be more effective to allow him to try and discover information instead of going around and arresting Dom. The other idea is that the police might not have enough to arrest him. Dom was not the one driving when they found him and other than racing, it might be tough to arrest him.
Lummie ★
Cops are usually completely unaware of an undercover cop's identity. The more, realistic reason is that the cop didn't ID Dom and since Brian's car was later destroyed, there's nothing for them to investigate. Afterwards, they might ID Dom, but there's an investigation on him, so they'd leave him alone.