I think LE searched the most likely disposal areas around Lisa's house first off (not the full river though - imo, nearly impossible and Lisa would have moved quickly with the water). Maybe those early ground searches were a result of phone pings, or just geographic profiling. They searched the woods, the landfill. They also did door-to-door interviews and searches, including abandoned houses within the search perimeter, which would include houses that Jersey might have squatted in (and maybe they first searched those that they knew he had squatted in). Now, according to reports, the area near where motorcylce man MT claims to have sighted a man in all white, with a female baby at 4 a.m., is being searched again.
Imo, all of these searches are important and could turn up something. But, they are important even if nothing is turned up. Whether or not LE believes someone is a valid suspect or a sighting is credible, they need to be sure so they can eliminate possibilities and so that a future defense team cannot claim that LE did not consider and investigate other reasonable scenarios. JMO...