BIB so how did Helen and Boris end up underneath 9 inches of crust ( sorry, not nice to type that ) in the space of 3 months. Would there be enough waste matter going into the tank in that time to form this layer ?
Somehow I cant see IS taking the time to put the body underneath this crust, as he was not expecting the tank to ever be checked.
I think they probably crashed through it, I doubt it would take the weight of a person, the police officer could break it up with a hoe.
I did wonder if Boris may not have been submerged though as it sounds like his body was much more decomposed than Helen's.