[Column] Issues and Academic Review Surrounding the Prosecution's Supplementary Investigation Authority

The procedures for punishing crimes closely connected to everyday life, such as assault, theft, and fraud, generally follow the order of police investigation → referral to the prosecution → supplementary investigation (if necessary) → indictment (referral to trial) → court verdict. In the modern constitutional order, criminal punishment is finalized only through a court ruling, making indictment-which can lead to a guilty verdict-the core step, and indictment itself is rooted in the investigative process.

The recent issue surrounding the prosecution's supplementary investigation authority concerns whether prosecutors can directly investigate cases in which the police have decided not to refer the case and the complainant files an objection, as well as whether prosecutors can conduct their own investigations in cases referred by the police if they deem indictment difficult based solely on the police investigation. Ultimately, the key issue is to what extent prosecutors should be recognized as the principal agents of investigations that can lead to a guilty verdict.

Some argue that the scope of supplementary investigation authority should be reduced to curb the excessive concentration of prosecutorial power, strengthen checks and balances among state agencies, and reduce the risk of human rights violations. Discussions about separating investigative and prosecutorial powers, strengthening the police’s primary investigative authority, and the debates on the complete deprivation or restoration of the prosecution’s investigative powers have emerged in this context.

However, the opposing side emphasizes that indictment is the starting point of an investigation that enables a court’s guilty verdict. Especially considering that victims need a practical channel for protection in cases where the police decide not to refer the case, critics point out that completely excluding prosecutors from the investigative process is unrealistic. If the essence of investigation is both to uncover the facts of a crime and to clearly establish the absence of a crime, then there is a logical basis for institutionally allowing a certain degree of prosecutorial involvement in investigations.

Examining this issue more deeply leads to questions at the constitutional level: Why must the state investigate crimes to the very end? Even without invoking social contract theory, the state exists to protect the lives, property, and freedom of its citizens. The Korean Constitution declares the state’s duty to guarantee fundamental rights in Article 10, and specifies the right of criminal victims to testify in trial procedures and the obligation to protect crime victims in Article 27(5) and Article 30.

The Constitutional Court also ruled in 1989 that "the state must protect its citizens by preventing the occurrence of crimes and, when crimes do occur, investigating the perpetrators and exercising the right to punish." The 2009 decision that found the statute of limitations for prosecution under the Special Act on Traffic Accident Handling unconstitutional is another example confirming that the exercise of the state’s punitive authority is central to guaranteeing citizens’ fundamental rights.

The driving force behind economic growth has also depended on the belief that "my rights are protected by the state." However, if the prosecution’s supplementary investigation authority is completely abolished, this belief could be shaken. At a prosecution reform seminar hosted by the Korean Association of Victimology in September 2025, a sexual assault victim testified that after the police decided not to refer her case, the prosecutor swiftly imposed an overseas travel ban and executed an arrest, ultimately saving her life.

In summary, the debate over restructuring the prosecution’s supplementary investigation authority should be approached from the perspective of protecting citizens’ fundamental rights, not political interests. While rational adjustments to prevent the excessive concentration of prosecutorial power are necessary, completely abolishing supplementary investigation authority risks weakening a crucial institutional shield that protects citizens from the threat of crime. Rather than extreme maintenance or complete abolition, a carefully designed system that ensures both victim protection and human rights is required.

The prosecution’s supplementary investigation authority stands at the intersection of the state’s punitive power and the guarantee of citizens’ fundamental rights. Future discussions on the structure of investigations must be based on academic and constitutional analysis and the practical standard of citizen protection, rather than political logic. In the final stages of designing investigative authority adjustments, it is essential to ensure this balance so that ordinary citizens can exercise their abilities without fear of crime.

Sangsoo Jung, Professor at Chungbuk National University School of Law