I believe just the opposite. I think if an amateur were going to stage a bloody sock, the sock would have more blood on it than one that just picked up the blood in the course of the crime. Lay people always think it takes more blood to look authentic. I think Darlie was wearing that sock and probably its mate and at some point she feared it would incriminate her if found at the scene, and that Darin was probably given the responsibilty of disposing of it down the sewer and just dropped it accidentally. I agree with the FBI profiler on this one. I think it they had planted the sock to be found by police, they would have left it closer to the house to make sure police would find it. The reason that sock doesn't fit into the rest of the crime scene is because it was not supposed to be found.