Should police keep info on record (incl DNA) if person is innocent?
Definitely not! (IMHO, of course). However benign the current administration may be, constructing an apparatus that would make life easier for despots has always been a bad move.
I think the continuum between a citizen's state and a police state starts at one end with the police being required to work for the well-being of the citizens, and ends at the other extreme with the citizens being required to act for the convenience of the police.
Any real-life polity is always going to be a sliding compromise between the two extremes, but I favour the more citizen-oriented end.
Therefore I reckon that the info the state has on individuals should be limited to
a; info that the individual doesn't mind sharing with everybody.
b; info on persons currently suspected of involvement in criminal activities for which the info would be relevant,
c; info that the individual needs the state to know, but which that individual wishes to keep otherwise private. (examples may be health records, tax statements.)