A friend of mine was put on a watchlist for evading arrest...?

So a friend of mine was supposedly speeding on a highway and "outran" the state trooper. He was pulled over a few days later and he was warned about it and that he was "on a watchlist" along with several other of his cars and he was told that they think he has done this more than once. They have one traffic photo of a car identical to his but you cannot read the plate, see inside, or any of the stickers that his car has on it. Would selling the car be a bad move? Should he go to the police station and ask for more proof?