What's the point of an investigation if it isn't to secure a conviction in a court of law? If prosecutors only prove that Barry Morphew was "overwhelmingly likely" the cause of harm to Suzanne (which is akin to a "clear and convincing evidence" standard), then he's "not guilty," since the criminal standard is "beyond a reasonable doubt."
I don't think Suzanne was abducted, harmed by wildlife, was hit by a car, etc. From my point of view -- a legal one, admittedly -- I want to see what actual evidence they have connecting Barry Morphew to Suzanne's disappearance. I also have no idea whether investigators screwed up: they have kept the details of the investigation to themselves (BTW, so have the Delphi murder investigators...and here we are 3 years since Abby & Libby were murdered).
I'm also at a loss at all the "reading" of Barry's demeanor. Very few people will have the experience of having their spouse go missing. Given this, why do we have a standard "expected" behavior for such a situation. In other words, whatever Barry's demeanor may be, I'm unsure it provides anything one way or the other.