Re: the phone locating the owner - that relies on multiple phone cells with overlapping edges so you can tell, by how long communication from mast to phone takes, how far the phone is from that mast. That allows you to triangulate location, as long as there are multiple masts. It's not clear to me how many masts there are in Rothesay (only one comes up on a google search, i tried my own area with the same query and it was accurate in the sense that it picked out the masts i know to exist), but if there aren't many it's possible that he was closest to one mast at all three locations (home, the Ardbeg rd, the murder site). GPS is far more useful, but only if the owner of the phone has it activated.