I know that they have always at least considered the possibility that he could be there; remember early reports from when he first disappeared stated that people were seen in the Food Lion parking lot? As for why they've focused so much on the river, I'm not sure. Maybe because the landfill wasn't going anywhere, but if he was in the river, they had to search that immediately or his body could be carried anywhere...I know that they "marked off" the area of the landfill where the trash from that area went and no new trash has been dumped there since, so hopefully if he's there, they'll find him.
So sad and frustrating that SOMEONE knows where he is and wont talk...