Yes, he did murder a guy-and please writers, must we have every Wesen perp inflict the most extreme act on their victims each and every week?
Well, the one who committed the murder was the "she" personality, I think, making it even more of an injustice to make Linus serve the time, given that there seem to be two distinct personalities inside the body. (Which is itself a pretty ridiculous portrayal of hermaphroditism, and inconsistent with any previous Wesen shapechanging ability we've seen -- although I guess there have been some murmurings about the Wesen form being a sort of second personality coexisting with the human form, but nothing as separate as this.)
As for Renard not knowing everything Wesen related, I suppose we have to accept that all Wesen aren't familiar with every single member of the species. Perhaps because he wasn't reared by the Royals, he didn't receive the education regarding the various members of the culture he might have gotten, if the family hadn't tried to kill him and his mother. Who knows?
Maybe, but he's been a Wesen cop long enough to become captain, and he's immersed in the politics of his world. It stands to reason that he'd know more about Wesen than Monroe and Rosalee, who are Nick's usual sources on Wesenalia aside from the books. And yet he seems clueless about things that Monrosalee are well-versed in. That just seems implausible. It made sense in season one when we thought he was the bad guy -- he was just obstructing Nick's investigations by not revealing what he knew. But now they're all on the same side, so he just seems to have an odd lack of knowledge about his own people.
And I may have blinked or was distracted, but did Alexis Denisoff actually appear in this episode? We heard his voice, but I at least, never saw him.
Nope, just the voiceover. Presumably his schedule couldn't accommodate appearing on the set the week this was filmed, and he recorded the voiceover later, probably when he came in for the next episode where he appears.