I don't think there is a connection. It is pretty obvious that the DK "just moved in" when you first arrive at the Tower while the dagger has supposedly been there for almost a century or so.
From what I read about fiends in later editions, the Demon Knight might be trying to set up a situation that enables him to enslave Aec upon release: the Demon Knight thus keeps him locked into the dagger until then, as he's too valuable to waste.
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It is pretty obvious that the DK "just moved in" when you first arrive at the Tower while the dagger has supposedly been there for almost a century or so.