The author does not offer the claim about Ziegler’s consulting work as evidence Ziegler is innocent. So, the author does not assume that this consulting work is relevant to being guilty or innocent.

The argument is not based on evidence against Ziegler’s being sane. It’s based on the claim that there’s a lack of evidence that Ziegler was sane. Also, the argument does not conclude that there’s a lack of evidence of Ziegler’s sanity. It concludes that Ziegler was insane.

The author concludes that Ziegler was insane at the time of the shot. If he was also insane when he worked as a consultant, that doesn’t suggest Ziegler might have been sane at the time of the shot. So, the possibility described by (C) does not undermine the author’s reasoning.

Moral responsibility has nothing to do with the argument. The author’s conclusion is that Ziegler was insane at the time he fired the shot. The conclusion is not that Ziegler shouldn’t be held morally responsible.

The accusers have submitted evidence that Ziegler was sane after the shot. If this constitutes evidence that Ziegler was sane at the time of the shot, then the author’s conclusion doesn’t follow from the premises.