1To turn oneself in to the authorities; to surrender oneself and admit (one's wrongdoing) to police.
容疑者は罪を認め、昨夜遅くに警察に自首した。
The suspect admitted the crime and turned himself in to the police late last night.
彼は弁護士と相談して自首することを決めた。
After consulting a lawyer he decided to surrender himself.
罪を犯してから自首するかどうかで家族と意見が分かれた。
The family was divided over whether he should turn himself in after committing the offense.