Sure they destroy them, they promise. 
Sometimes, 47 criminals must go free to save the one million innocent people from living in a police state.
From what I’ve heard, here in Maine, there is a state law requiring police to destroy these records after 30 days.
I have the sneaking suspicion that if one of us were to go around photographing and recording and databasing plate numbers on police cars, they’d suddenly find a reason to be upset with it.
Sure they destroy them, they promise.