[He'll offer no thanks, but only an acknowledging nod.]

In that case... I'm not sure there's much more to figure out about Zack's involvement. He was pretty forthcoming yesterday about his role in killing Nanami first, so I'm not sure there's much more to follow in that vein. Unless it's all an elaborate lie, which I doubt, there's not much more for him to hide if he'd come out and say all of that in the first place.

So there might be some significance to the first murder still, but the second murder is what we need to focus on.