Is there an old septic tank on the property? Sometimes folks get a second one and abandon the first. He could have filled it with cement or lye.
Just thinkin’
It is very possible.
I know the investigators researched the history of the land - all the old deeds and that sort of thing.
Whatever he did - he did it within 3 to 4 hours and then tried to pretend he didn’t have a care in the world.
He briefly cracked when the police put out a false report that the body was found on the property.
His first response was “there is absolutely no way they found her”
He stuck with that for most of the day.
As time went on his question was “did they find dna? did they find semen on the body?”