Wow is this case intriguing! I took a step back and started mapping things associated with this missing couple along with previous fire records to see if I could find any patterns. Put it this way, I wouldn't want to live near them, there's a scary amount of fires/arson incidents in that location. I've also come across some not-very-confidence-inspiring information regarding the local LE (Google them, you'll be surprised!)
Here's a link to the map. I've got as a far as April 2015 for fire/arson incidents & will finish it off. I would love to also map "peeping Tom" incidents & (as much as I'd hate it) animal cruelty incidents because my mind is going: Animal cruelty---->Voyeurism---->Arson---->GBH/ABH/Physical attacks---->Murder and so far it
could be said that we can tick off 2 possibly 3 of these if 1 person is responsible for the lot...
Please PM me if I've missed anything you think should be added