[ She is being a detective. A hanging one, unfortunately. It's throwing her off. ]

He's the only one with something that shade of blue, the ribbon is only important to him, and as we don't see any other bloody corpses, clearly Albel-san didn't manage to frame anyone like Diego-san is implying he tried to. The question is still "how did Albel-san die, and why does nobody else match the clues presented"?

Sometimes the obvious answer is indeed the correct one.