[Alamo-Girl]

I believe his mother passed on in 1997. And as I recall, he remembered Terri's will in the matter sometime after that...

[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.