Number should have been traceable. Hope the Po-Po snagged it at the time of the call.
It probably came from an office at Police HQ’s.
These are done using burner phones.
For the Federales, yes. It can get quite expensive to do that, but they have the technical skills and infrastructure access to trace such calls. They will if they are told to do so. They won't get those instructions when the victim is politically incorrect.
For the local cops, no. A burner phone or an IP phone call are easy for a perpetrator to setup and basically impossible for the locals to trace. They only catch the perps if they brag about what they just did, and an acquaintance turns them in. Which does happen occasionally.