Circumstantial, yes. But it is a LOT of circumstantial evidence.
The Ivins theory of the case is the one theory so far proposed that best fits the known facts.
Of course, that is where the argument becomes epistemological. Whence comes our ‘knowledge’ of these facts? Previously, our understanding of the ‘facts’ in this case came from respected ‘authorities’ such as Barbara Hatch Rosenberg (Federation of American Scientists), Don Foster, PhD (identifier of “Anonymous” Joe Klein) and Pulitzer Prize-winning NYT journalist Nicholas Kristof. How much more credible and authoritative can one be? And yet, QED, they were mostly full of crap.
Now our “facts” are being fed to us by... the Feds. They haven’t covered themselves in glory either. Who, and what, to believe?
It is not unlike Schrodinger’s Cat. Ivins did, or Ivins didn’t. Ivins did AND didn’t. We can’t know until we look in Schrodinger’s box. Unfortunately, the Feds are the keepers of the box, and we aren’t going to get a direct view inside.
Are there possible alternative explanations? Sure. However, the Ivins theory is the one that makes the most sense when laid alongside the meager few independently verifiable facts. That is good enough for Ed, and coincidentally, me. That is, at least until we can get a look inside the box. But for now, I won’t lose sleep.