There is something odd about having unmarked cars with non-uniformed police officers assigned the job of questioning people.
First, it leads to accidents like this. Second, what’s the point of being undercover if you supposedly are going to jump out of your car with badges and yelling “police”? That will blow your cover.
They had the guy’s car and license plate, they should have phoned it in an had a marked car pull him over for questioning. Or they could have driven after him and pulled him over with their siren, which would make it more clear they were cops.
Curious that you would characterize this as an accident.