Yoon’s defence minister, Kim Yong-hyun, resigned on Thursday and took full responsibility for the martial law declaration.
It was Kim who suggested martial law to Yoon, Interior Minister Lee Sang-min told the parliament hearing. South Korean media have carried similar reports.
It became clear during the hearing that few knew about Yoon’s plan. The vice defence minister, Kim Seon-ho, said he learnt about it on the news.
Army chief Park An-su said he had been handed the text of the martial law notice only on Tuesday night.
“There were four of us who were reviewing the draft… While we are military experts, we are not experts on martial law. Time was passing and we were all saying ‘what are we to do, what are we to do?’ he told MPs.
A motion to impeach Yoon was tabled in parliament late on Wednesday, and South Korean law requires that it be put to a vote within 72 hours.
The main opposition Democratic Party is pushing for a vote on Saturday evening.
If the impeachment is approved, the president will be immediately suspended from office, while the prime minister becomes acting president.
A trial will then be held before the Constitutional Court, a nine-member council that oversees South Korea’s branches of government. The process could take up to 180 days.
If six of the court’s members vote to sustain the impeachment, the president will be removed from office.