LogFAQs > #920679219

Apparently everyone has an "alibi" because those in the guest house couldn't have come deliver a letter

And we know Natsuhi and Krauss didn't do it

So either Genji did (very possible, clearly the guy will just do literally anything he's told, his morals actually suck for someone so "noble")

Or those guest house alibis aren't as strong as they say. Which seems likely. "The doors were locked" whatever, anyone could sneak out.