A DevAddr is not unique, there are simply not enough of them to make them unique. Multiple devices in the world will have the same DevAddr at any given time. TTN would be able to find which DevAddr belongs to which device given the entire uplink data packet but only at the time of transmission because some of the information required will change over time.
If the police want to investigate they will need a ‘tap’ at TTN level, not the limited information you can provide.
You may want to search the forum as there have been discussions regarding the subject in the past as well.
For instance: Legal problems setting up gateways on public buildings