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surrender (to the authorities); giving oneself up; turning oneself in
犯人は罪の意識に耐えられず警察に自首した。
The criminal could not bear the guilt and turned himself in to the police.
弁護士の勧めで自首することを決意した。
I decided to turn myself in on my lawyer's advice.
自首すれば刑が軽くなる可能性があると聞いた。
I heard that turning yourself in may result in a lighter sentence.