Yes. You would need a warrant for that. I meant in this case they could have easily obtained one. The had the IP, which is how they got IMSI.

I imagine you'd use Stingrays when you want to cast a broad net, i.e. who are the persons who are within X distance of the tracker and were also around at a previous location.

So I can't imagine why they would have wanted to use the Stingray here.