A. Article 12(3) of the Constitution provides that "warrants issued by a judge through due procedure upon the request of a prosecutor shall be presented in case of arrest, detention, seizure or search," and Article 16 provides that "in case of search or seizure in a residence, a warrant issued by a judge upon the request of a prosecutor shall be presented," thereby guaranteeing the warrant requirement at the constitutional level.

The warrant requirement our Constitution has adopted is the principle that, in criminal proceedings, compulsory measures of arrest, detention, seizure and search must be based on a warrant issued by a judge whose status is guaranteed by judicial independence. Therefore, the essence of the constitutional warrant requirement lies in requiring that a neutral judge make a concrete determination before compulsory measures restricting fundamental rights, such as arrest, detention, seizure and search, are taken. Meanwhile, in enacting laws on investigative agencies' compulsory measures against suspects, the legislature may, within the scope of complying with Article 12(3) of the Constitution as a special constitutional provision, comprehensively review the legal reality of our society, investigative practice, and the level of legal awareness of investigative agencies and citizens, and then make various policy choices according to specific circumstances. Constitutional Court, May 31, 2012, 2010Heonma672.

B. A request for communication confirmation data that permits base-station investigation is an investigative method that, with the court's permission, allows a request to a third party, the telecommunications business operator, to provide communication confirmation data on a subscriber without that subscriber's consent or approval; since it is a compulsory measure under the Protection of Communications Secrets Act, the constitutional warrant requirement applies. Communication confirmation data is mainly used at the initial stage of starting a criminal investigation; in particular, where a crime occurred at a specific time and place but the investigative agency has found no leads, using all phone numbers that placed calls through a specific base station during that time as investigative leads can be useful for narrowing down suspects and arresting them or collecting related evidence. In this respect, it is hard to deny that, in investigative practice, there is a real need to permit base-station investigation for crime prevention and early resolution of cases. Accordingly, the permission clause in this case, comprehensively considering the need for base-station investigation, the demands of discovering the substantive truth and investigating crimes swiftly, the characteristics of communication confirmation data, and investigative realities, allows investigative agencies, with the court's permission, to request communication confirmation data such as all phone numbers that placed calls through a specific base station during a specific time. Considering that the essence of the warrant requirement lies in requiring that a neutral judge with guaranteed personal and material independence make a concrete determination before compulsory measures are taken, the permission clause in this case, which requires the permission of the competent district court or branch court in the manner prescribed by the Protection of Communications Secrets Act, can be said to satisfy the warrant requirement in substance. Constitutional Court, full bench decision 2012Heonma538, rendered June 28, 2018.

C. Therefore, the permission clause in this case does not violate the constitutional warrant requirement.

Chapter 3 of the U.S. Electronic Communications Privacy Act governs pen registers and trap-and-trace devices. These cover records of communication use such as the phone numbers entered into a telephone to start a call, routing (the process of determining the path a sent message takes to its destination), addressing (connecting to or selecting the other party from a terminal), and location and access-point tracking, which correspond to communication confirmation data under Korea's Protection of Communications Secrets Act. The United States obtains such data using pen registers or trap-and-trace devices, and if it is determined that the purpose, "that the information likely to be obtained is relevant to an ongoing investigation," is met, an order authorizing installation of the device for a period not exceeding 60 days is issued.

After the decision of nonconformity with the Constitution, the National Assembly amended the Protection of Communications Secrets Act in December 2019, adding a supplementarity requirement so that requests for communication confirmation data on an unspecified large number of people, such as base-station investigations, and requests for real-time location-tracking data are allowed only where it is difficult by other means to prevent the commission of a crime, find or secure the offender, or collect or preserve evidence. Comparing the decision's reasoning with the amended provisions lets you persuasively describe the limits of restricting fundamental rights in constitutional law, criminal procedure and information law assignments. It is recommended to look at the provisions before and after the amendment side by side.