Here's my thought on something, and people probably aren't going to like me for it, BUT (I must add my info. could be wrong)
Depending on when Sam was last seen by family, surely they had to know the truck was missing as well. Why wasn't it ever mentioned that he could possibly be missing in this truck.
The neighbors said they saw the truck sitting for days....would they have called the police to report it, if they had known that the truck was suspected to be missing with the suspect. Everyone in Logan County was aware of the situation, and just letting people know he's on the loose would be enough to make everyone's eyes glued to every truck they would see.
Would they have been able to search for him sooner, possibly preventing the elderly couple from being missing?