Maybe phone records will tell. It's not like a marijuana hit is urgent.
The police are angry because this has revealed the staggering crime stats of that park..highest in the city. And it’s a small (but long) strip of land? Most of which is a cliff and unusable. But the school has tennis courts and facilities down there, so students do have lots of reasons to be there other than buying drugs. I doubt that she would be stupid enough to go look for a drug dealer there, and the stuff is certainly available on campus.
The police union is just angry because this makes them look bad.