It's more like you'd have a map with a line that shows where the terrorist has been, you can overlay on that map everywhere every other whatsapp user has been a

It's more like you'd have a map with a line that shows where the terrorist has been, you can overlay on that map everywhere every other whatsapp user has been and pull out any that spend a significant amount of time with the known terrorist. Then you know exactly who they associate with and can interrogate their profiles directly to see if they are viable suspects.