It's not easy, it's an investigation. I expect them to start with interviewing the victims, which will probably point them to some internet forums. Then it's about reading forums and identifying people and a zillion of other things that I can't think about because it's not my job (and so I already wrote too much.) Of course those investigators have other things to do but so do those SWAT teams. It's a DoS against the police.

If 911 can track calls, that would help, but I have no idea if they can, even in my own country.