The documents, found in the crisis management office at Cheong Wa Dae, included a daily journal from the office drafted April 16, 2014, when the passenger ferry sank in waters off the country's western coast, killing more than 300 people, according to Im Jong seok, the presidential chief of staff.
Im said the daily log showed the first report of the accident was made to then-President Park Geun-hye at 9:30 a.m., instead of at 10 a.m., as earlier claimed by the ousted leader and her aides.
The Cheong Wa Dae official said the document was revised Oct. 23, 2014, to say the first report was made at 10 a.m.
"The reason they pushed back the time of the first report to the president by half an hour appears to have been an attempt to reduce the time between the first report and Park's first order, said to have been made at around 10:15 a.m.," Im said at a press briefing, apparently suggesting a 45-minute gap between the first report and the first order would have aggravate criticism for her inaction during the accident that left 304 people dead.
The fresh allegations came as the local district court trying the ousted former leader Park is considering extending the time of her detention that is set to expire Monday. The former leader has been detained since March 31.
Whether the documents will lead to an extension of her arrest remains to be seen, but many have said fresh allegations may increase the possibility.
The court is expected to reach a decision on Park's detention Friday.
The tragic sinking of the passenger ferry partly triggered the start of candlelight vigils late last year that eventually led to the ouster of Park in March.
Many, including the bereaved families of the 304 people who were killed or went missing in the accident, demanded the former president to reveal her whereabouts on the day of the accident, claiming she may have failed to carry out her duty while being caught up in personal affairs.
Cheong Wa Dae said the documents discovered at its crisis management office also indicated the National Security Council may have altered its manual on crisis management, possibly to remove any blame that might fall on the former president.
Before what Im called an "illegal" revision of the manual, the NSC guideline cleared named the NSC as the top control tower in dealing with any major disaster or accident.
The printed phrase was crossed out with a red pen in late July, apparently at an instruction from then NSC chief Kim Kwan-jin, Im said.
A handwritten phrase was added in its place stating the NSC was to act as a control tower only in security-related incidents. The revised manual was then delivered all government offices, according to Im.
Such a revision apparently came after then presidential chief of staff Kim Ki-choon testified before the National Assembly that Cheong Wa Dae or the NSC were not the control tower in dealing with the ferry sinking, Im noted.
The incumbent presidential chief of staff also said such a revision to the NSC manual required legal procedures, including a review and approval by the Ministry of Government Legislation, but that the former administration took none of such steps.
"Cheong Wa Dae believes such an incident must never be repeated. Believing the incident represents the worst case of manipulation of power, the presidential office plans to request a formal investigation," Im said. (Yonhap)