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Keansor the spymaster never seemed to learn what the West did, that Morina became a maid in the palace. If he did he would've found her long ago. Without that key piece of information, he can investigate all he wants, but it won't go anywhere. He would never even connect the two - at best he'd connect her to the incidents around the palace, but even the crown prince has more or less figured that out. He essentially has nothing to investigate.
Edit: Now, if he's investigating why the West's emperor is there - which is probable - then he might stumble on their interrogation of the maids. From there all bets are off, but there is still no smoking gun.