The investigation is expected to focus on who issued the command to draft the martial law document and whether it was designed for implementation. The document was drafted in March last year when South Korea was engulfed by massive protests against former President Park Geun-hye.

Former Defense Minister Han Min-koo, who was reportedly briefed about the document by then-Defense Security Commander Cho Hyun-chun, claimed the document was simply a contingency plan in the event that protestors forced their way into the presidential office.

But President Moon Jae-in’s aides and his governing Democratic Party of Korea countered that the document was more of an implementation plan, as it is much more detailed than the military’s usual plan of overseeing a national emergency.

“The military is supposed to serve the people, but it was trying to point guns at the people. ... We will hold everyone involved accountable and find out whether they committed treason,” said Rep. Choo Mi-ae, the leader of the ruling Democratic Party, Monday.

Debate also continues to escalate over who instructed the Defense Security Command to draft the martial law document, which even included a plan to deploy tanks in downtown Seoul, censor the media and block lawmakers from ending the emergency action.

While Han and former Defense Security Commander Cho claimed there were no separate orders from higher-ups, doubts persists over whether security aides close to former President Park ordered the military to draw up an emergency plan.

Later in the day, human right activist groups filed a lawsuit against Han, former chief of the National Security Office Kim Kwan-jin and former chief of the Presidential Security Service Park Heung-ryul. All of them are retired four-star Army generals.

“We don’t think the Defense Security Command is the only agency involved (with drafting the martial law document). It was designed to overthrow the government,” said the Center for Military Human Rights Korea in a joint statement with other human right advocacy groups.

Meanwhile, an allegation has emerged that former Defense Minister Han ordered his staff to consider a plan to appoint the Army’s chief of staff as a martial law commander -- an indication that Han was more involved in drafting the controversial document than he has claimed.

According to Yonhap News Agency, an internal document was found showing that Han changed the military’s usual plan of appointing the chairman of the Joint Chiefs of Staff as a supreme commander overseeing a national emergency.

By Yeo Jun-suk(jasonyeo@heraldcorp.com)