The letters were sent by the CIO two weeks after it obtained warrants to search the presidential residence in Yongsan District, central Seoul, and take Yoon into custody over his short-lived imposition of martial law on Dec. 3.

A CIO-led attempt to execute the warrant on Jan. 3 failed in the face of resistance from a combined force of 200 PSS and military personnel who blocked investigators and police from gaining access to the presidential residence.