My husband was watching a program on the Discovery Channel about surveillance technology about two weeks ago and I sat down and watched part of it. The FBI has some sort of technology now that they can pick up conversations within a building just by aiming a device at the building. It was demonstrated and it's amazing! Knowing that the FBI is involved in this case, I wonder if LE had enough information (the Walmart receipt and other evidence) to pinpoint MH as the likely suspect and bring in their specialized equipment? They may have picked up MH making demands of Sarah.
When LE found the truck, MH was sitting in his car watching the truck. LE spoke to him. And then ran his plates, ID'ed him, got his prison record, found his address, found his prints on the truck & went to his house & listened.
He thought he was so clever. You can't win with LE - they have years of experience dealing with societies worst.