Essentially the crux of their “case” is that he had access to the particular variety of anthrax.
Nothing else. That’s supposed to imply causality. And Motive?
Oh, he’s a lone nut plagued by private demons.
Talk about feces on a shingle.
And he stayed late at night.
But they disavow any possibility that he may have provided spores to someone else (who refined them elsewhere).