I hadn't viewed the Under Investigation episode, so thank you Imstilla.grandma for your post.
A comment made by Nigel Phair, (who formerly headed investigations at the Australian High-Tech Crime Centre, (AHTCC)) is IMO of particular interest:
"That means someone's done something active against those two devices and you have to know what you are doing to think I'm going to completely take these out," he said.
"It's not just turning them off, it's destroying them and then getting rid of that piece of evidence."
Tampering with devices takes significant effort but Phair explained though criminals may attempt to change SIM cards, mobile phones, if on, are still traceable."
IMO this was therefore no random crime. IMO this was a professional hit rather than a hit-and-run accident or personal "crime of passion". Very carefully planned and organised by, well "organised" people.