A little hint which I observed while playing the game:

1.Whenever you're assigned to arrest smugglers, robbers, kidnappers etc.
  by scanning traffic, they will be always in yellow cars.
  So don't waste your time scanning the rest.

2.When you catch one, observe it.The others' cars will be of the same model.

3.Try to finish off the suspect in mini-game only, try not to go into pursuit.

It requires nothing else.The game is so easy that you can finish it off in 
one day only....