Others have commented the assassin is a time traveller. Time travel has nothing to do with it! Affect an unrelated thing in such a way that the knock on effect leads to the death of the intended victim.
"By the Gods! You love her, don't you?" Gibbs asks Captain Jack. He flinches, a horrified expression on his face.Gibbs, what do I do? I'm utterly terrified of her, of what she makes me feel.Where's the rum?
They all stared at her, unsure of how to react. They all knew now what she was capable of, and none of them - not even she - could predict when her careful control would finally crumble. They gambled with their lives every day they kept her here.