Have an independent non-profit with strong oversight manage the data. Grant access with a warrant.
The police should show that a crime has likely been committed, and get access to just the data that probably has evidence.
How do you do a warrant for a device that alerts when a car on a hotlist transits an intersection?
You still have people with very tempting access to a whole lot of data. I don't see how this is different from the current situation other than it's just different (corruptible) people with access.