It's very predictable down to the precise ethical lesson of the scene. Starlight must be involved, because she was raped and she must prove her strength. But she can't be a vigilante and kill him. On the other hand The Deep can't really be turned in to the police. How do you drag him in? How do you prove anything, it's her word (and she is now a known terrorist) against his. So justice via the courts is very unlikely. So she accidentally puts him in a situation that kills him.
Once you notice this trope, the good guy doesn't kill the bad guy, he is undone by circumstances that no one intended, you see it everywhere.
Because opposing vigilanteism is a CORE jew metanarrative.