He knows that he can kill her while she sleeps. She is vulnerable and oblivious as she lies there, alone, in her bed. He could pull the trigger any second and it would all be over. She'd never know what hit her; she would merely cease to exist.
He knows that he can get away with it. Of everyone on board the Dominion, he has the highest standing with the Earth Alliance forces. No one would ever dream that he would do something as horrible as killing his captain. And he could so easily shift the blame to another person. If he said that Orga, Shani or Clotho were responsible for her death, they would believe him. It would be that easy – almost too easy – to cover it up.
He hates Natarle Badgiruel. He hates her for disobeying him, he hates her for her arrogance, he hates her for her beliefs. He hates everything about her, and as he stands in the entryway to the captain's dorm late at night, knowing everyone else is asleep, he rests a hand on his gun and knows that he could dispose of her right there.
Yet every night, after he stays there for hours just observing her, knowing he has all the power in the world, he can be found stalking silently away. No damage is done. His hatred is his power, and he must control his power, lest it become dangerous. It is his secret, and when the right moment comes, he will finally set it free.