The military has since formed a special investigation team comprising about 30 prosecutors and investigators from the Navy and the Air Force. The team will complete the necessary preparations on Sunday and launch an investigation on Monday, officials said.

"We're going to conduct a fair and thorough investigation according to law and principle," an official said.

Those subject to the investigation are expected to include the then DSC commander, Cho Hyun-chun, then-Defense Minister Han Min-koo and Kim Kwan-jin, chief of the presidential National Security Office at the time. Then-Prime Minister Hwang Kyo-ahn and jailed former President Park Geun-hye could also face an investigation.

Incumbent Defense Minister Song Young-moon is also expected to face an investigation. Song has come under fire for doing nothing even after he was briefed about the DSC document in March this year. Some opposition lawmakers have called for his resignation.

Criticism of Song rose further Sunday as he was found to have falsely claimed that he had an unidentified "outside agency"

conduct a legal review of the DSC document. Song appeared to have made the claim in an attempt to avoid criticism for doing nothing about it.

But on Sunday, the Board of Audit and Inspection revealed that when its chief Choi Jae-hyeong met Song at the March 18 closing ceremony of the PyeongChang Paralympics, the defense chief talked about an unspecified military document about mobilizing armed forces at the time of the impeachment trial, but the ministry never asked the agency for an official legal review of the DSC document.

The DSC document outlines ways to impose wartime martial law in case the Constitutional Court rejected the National Assembly's impeachment of Park and kept her in office. It also suggested mobilizing hundreds of tanks and thousands of troops to impose martial law.

But the plans in the document were not carried out because Park's impeachment was upheld.

The special investigation team also plans to look into suspicions that the DSC spied on the families of victims who were killed in the tragic 2014 sinking of the ferry Sewol and conducted operations to foster public opinion in favor of the then-conservative government. (Yonhap)