The official report is here:
https://www.tsb.gc.ca/eng/rapports-r.../a21o0069.html
The Toronto Buttonville Airport (CYKZ) is a very busy GA airport, particularly for flight training. In years past it was known to be the third busiest airport in Canada, though that is less so now. The approach to runway 15 is the second most common approach flown there (33 being the most common), so nothing the least unusual about a 172 flying a circuit to runway 15, it's been being done there since the 1950's! The police force involved operate their helicopter from that airport, so the environment is (should be) very well known to that police department. In any case, the police were "told", and hopefully do better with their drone operations in the future!