Here is another source:
https://threadreaderapp.com/thread/1866500696260145330.html
To arrest key liberal leaders including Lee Jae-myung, the military dispatched the HID unit, the special forces whose main task is to assassinate major North Korean leaders in case of a war. They are normally near the DMZ, but were just outside of Seoul on Dec 3.
The HID unit were not dressed in the ROK military uniform. Instead, they were given a false North Korean uniform. The plan was to have the HID unit either assassinate Lee and others, and if that failed, have the "rescuing" South Korean soldiers to kill both Lee and the HID unit.
The Defense Minister's original plan was to provoke an attack from North Korea, then use that as an excuse to declare martial law. To that end, South Korean military flew several drones over the Pyongyang sky, spraying propaganda fliers. North Korea did not attack, however.
;)