The presidential office says it has found a data file suggesting officials under the previous Park Geun-hye administration fabricated a situation report on the sinking of the Sewol ferry in 2014.
The document is said to have been fixed six months after the disaster to indicate that the now-impeached former president was informed about the sinking 30 minutes later than she was actually told about it.
Presidential Chief of Staff Im Jong-seok on Thursday told reporters that the file suggests modifications were made to change the initial report time from 9:30 a.m. to 10:00 a.m. on April 16th, 2014 - the day the ill-fated ship capsized.
The former administration had claimed Park was informed about the sinking at 10 a.m. and issued her first instructions 15 minutes later.
The previous administration was criticized for its ineffective initial response to the sinking that killed more than 300 people.
Im said incumbent government staff discovered the file on a computer system at the top office's National Security Office.
The chief secretary also said another file was found in a cabinet at an underground bunker at the presidential office that suggests the previous administration illegally fixed national security management guidelines.
Im said that the guidelines were fixed a month after the sinking to indicate that the Ministry of the Interior and Safety was responsible for public safety issues although it was the National Security Office of the presidential office that was in charge.