One of the cases that I follow, a man went missing, along with his cellphone and vehicle. His vehicle was found several days later, and CCTV in the area showed a man walking and then running away from the truck. Although they never recovered the man nor the cellphone, they were getting pings from his cellphone for a period of time after he'd gone missing. But I don't think they discovered this until after the truck was found, and perhaps that is because they then had a cellphone tower to check against? I'm not sure how that works. ie I'm not sure they can say, 'I have this phone number, can you tell me if it pinged ANYWHERE, during this time'... or if they would be much more successful asking, 'I have this cellphone number AND this location, can you tell me if cellphone towers in THAT area received any pings from that number during this timeframe'... so in a case like this.. where they have no cellphone numbers really.. would they go to the nearest towers and ask for printouts of pings that came from them, and try to match them up? I have no idea, but very interesting. The cellphone numbers that they DO have, I'm sure could be checked against the local cellphone towers, so that is at least a way to check out the people they already know of. ?