After allegations of concealment of evidence and poor investigation of the high school girl murderer ‘Jang Yoon-gi case’, voices calling for the prosecution to retain supplementary investigative authority have grown louder. However, the Democratic Party insists on ‘complete abolition’ and is putting forward as an alternative the strengthening of the ‘right to request supplementary investigation’, which allows prosecutors to request a supplementary investigation from the police. Let’s look into measures to prevent another ‘Jang Yoon-ki incident’.