It IS kinda Matilda's fault for leaving out important details, like who was asking to see Harlein. Her sudden excitement was funny, and she couldn't have been more obvious about wanting to be Elma's new boss.
Anyway, not much to say about the rest of the stuff in this chapter. It's just more of the investigation going forward. Hilde's master Kalos is still not in the clear, and Luce and Elma's look last chapter seems to say they both suspect her too.