[Robert A Cook PE]

I think this linkage (finding out that he has the ability to kill his parents, thus showing him how to get rid of Terri through the "proper" doctor and the "proper" lawyer) is an important link in establishing the circumstantial evidence:

Method.

Motive.

Opportunity.

[Alamo-Girl]

Indeed. If the case were pursued by a prosecutor, I imagine your point would be raised to the jury!