Hmm.
I think he was in a rage when darting around "shooting chipmunks" (or squirrels or whatever - none of them needed to be shot). But was she dead at that point? I am on the fence. I think he might well have tranquilized her.
And then...killed her later. Which is not a fit of rage, IMO (unless, of course, he's one of those people who can sustain rage for many hours). He started the process of killing her in a rage (but had already fantasized/thought through how to kill her).
If he did strangle her, I think it happened off-premises. I've always thought this. And I think it's an attempt at creating the "perfect murder" and that part of it was thought out before. Or he's incredibly cagey and smarter than I think he is.
I'm very interested in rage (have never experienced it, myself; but have seen it). It's usually brief and the rageful person often makes lots of mistakes (like Barry). But he was not in a rage the whole time.
I'd like to think that most of us would just collapse, and turn ourselves in, or otherwise let others see a bit of who we truly are - if we found that during a rage, we had killed someone.
Ms SD will be crucial at trial. She knows and knew a lot.
IMO.