The Jamison Family

The Jamisons disappeared on a warm October day. It would be four years before their bodies were discovered. They were not missed for several days; neither worked and Madyson was home schooled. They were known for setting off at short notice and without informing friends and family. Nobody really noticed their absence, at first. When their disappearance finally reached the ears of the police, they set out to find what had happened to the family.
The white pick-up truck in which they travelled was not going to be easy to hide, and indeed, it was eventually discovered a few days later, parked - maybe - in a clearing off the road. It was about a mile from this spot that their decomposed bodies would eventually be found four years on. What happened to the Jamison Family??