The entities holding the information here are literally police departments. The information itself is evidence, used in active criminal investigations. It's good to want things, though.
It's a bit like saying pornography is used in the study of human anatomy.
I was replying to the "used in active criminal investigations" part. Yes, the ALPR data managed by Flock is sometimes used in active criminal investigations. However, it's also used for many other things.
The many other things that it's used for supports ~jedberg's argument.
It's also easy to imagine reasonable compromises, like a time delay where they only have to report after e.g. 48 hours, and allowing a system whereby a judge can issue a warrant to extend that delay.
I watched ALPR proponents in Oak Park make exactly those kinds of arguments.