One thing that has stuck with me after SM's trial is his last few comments as he was replying to the judge and family about not being able to give the answers that the family needs as to Heather's whereabouts.
JMO
The way he said things has me thinking that whatever they did with Heather has caused her body to not be recoverable.
Whether that means they took her out to the Ocean by boat and sunk her body by attaching an anchor or other weights,
or whether it means they used a large fire to burn up most of the remains,
or whether they used some other means to get rid of her body,
the way he talked about not being able to give the family information about where the body is has me thinking that their disposal method means her body is not recoverable.
Thinking his statements can help narrow down what they actually did with her.