What was the motive behind Matthew Farwell's alleged murder of Sandra Birchmore?

A significant motive in this case appears to be Matthew Farwell's complicated personal life. Farwell was married with children, and his wife actually gave birth around the same time that Sandra Birchmore died. This created a precarious situation as Farwell was simultaneously having an affair with Sandra, who was pregnant, presumably with his child. The timing of these events suggests that Farwell was facing the prospect of his affair becoming public and having to acknowledge a child from this relationship while his wife had just delivered their own child. This converging circumstance likely created immense pressure that prosecutors believe motivated the alleged murder.