Prosecutors announced Sunday that President Yoon Suk-yeol has been officially named a suspect in a treason investigation related to his short-lived martial law declaration on Dec. 3. This marks the first time in South Korea’s history that a sitting president is under criminal investigation while still in office.

Investigators are now focusing on whether Yoon’s actions violated constitutional provisions and military law, with the Special Investigation Headquarters confirming plans to expand its inquiry into other officials involved in the declaration.

Yoon stated in a public addresson Saturday that he would not avoid “legal or political responsibility” for the declaration.