If it's a terrorist cell doing this then they have the $$$ for the kind of toys it takes to bounce calls in a manner that the call won't be traced. If the phone number is a U.S. number or in other modern nation, fuggedaboudit. Calls from/to/through it WILL be traced.
OTOH, if it is off some ancient Strowger switch exchange in Indonesia...
That's what I was thinking too, an overseas number.
I reiterate (say again for those of you in Reolindo) calls can be bounced and yes they will pin register however, to someone with even simple hacker skills calls can be routed with dead ends. They ping to CO's and simply get lost.
Either way, I hope they catch this (these) folks soon.
I have my doubts though if the FBI is now involved.