There's plenty of opportunity to move and conceal a body using the hypothesis of the dog findings. Tracking people's possible movements on the night against the timetable. The men split up - opportunity is there to move and conceal if you're alone i.e. Smithman. There's opportunity at other times - on checks (insider), not on checks (abductor), before tapas, later again in private searches etc. Kate is correct in her book that it becomes one word against the other but if you can id Smithman then his movements may reveal themselves for all to see when you compare it against the timetable of events that night gathered from the statements and evidence collected e.g. Smithman was last scene going in the direction of the church when he past the Smith family. In this hypothesis, knowing where Smithman finally concealed the body is the hard part and most probably only he can answer that unless more evidence presents itself.