The site they chose to dig up is a huge clue. It is probably the septic area as other posters have mentioned. The diggers were in and out of there fast, remember that suprised us all. Excavating looking for a body is time consuming, you have to be careful- so they weren't looking for a body. But it makes complete sense if they were just trying to access the septic system and gray water system and maybe remove a piece of the outgoing pipe from the house or filter to test for DNA or other evidence. If he used the sinks in his house to clean up, evidence goes down the drain. I know in other cases they have taken sections of pipe from the house. That being said my guess is this is more of a hands on crime without alot of need for clean up. JMO. The short length of time the diggers were being used for tells us something though.