I mean this as a serious suggestion (not trying to be flippant/snarky). Maybe someone paid attention to Tricia's interview with MR. He only mentioned searching by himself in two locations -- the area around the lake and the place Dylan's remains were actually found.
Well, as I recall, police did take his truck(s) then returned. Hopefully they stuck a tracking device somewhere on that truck.
To see as to exactly where was he going.