Suh Hoon, left, and Park Jie-won, former heads of the National Intelligence Service / Yonhap

Prosecutors said Thursday they have begun investigating two former chiefs of the state spy agency over allegations they mishandled two separate incidents involving North Korea, allegedly to curry favor with Pyongyang.

The Seoul Central District Prosecutors Office said it has allocated the cases of Park Jie-won, a former head of the National Intelligence Service (NIS), and his predecessor, Suh Hoon, to two separate teams. The two served as the NIS chiefs under the former Moon Jae-in administration.

On Wednesday, the NIS filed a complaint against Park for deleting intelligence-related reports without authorization in regard to North Korea's killing of a South Korean fisheries official in September 2020.

The 47-year-old official, Lee Dae-jun, was fatally shot by the North's coast guard near the Yellow Sea border between the two Koreas, a day after going missing while on duty on board a fishery inspection boat.

The then government of President Moon Jae-in concluded at the time that the official was killed while attempting to defect to the North, but that conclusion was overturned last month as the Coast Guard announced it has found no concrete evidence backing the defection allegations.

Park served as the NIS chief from July 2020 to May 2022 until President Yoon Suk-yeol took office.

The former spy chief flatly denied the allegations in a radio interview with CBS, claiming it is impossible to delete the original file stored at the NIS server, and if he did so, it would leave a record of the deletion.

"Why would I do such a foolish thing?," Park said, adding no NIS director or an official would commit such an act when they can be imprisoned after a new government takes office and checks the record.

Separately, the NIS also requested the prosecution look into a suspicion that Suh ordered an early end to an internal investigation into the case of two North Korean fishermen who were sent back to the North in November 2019 after being captured near the eastern inter-Korean sea border.

The investigation into a North Korean defector usually takes between 15 days and one month, but the probe at the time only took around three to four days.

Suh worked as head of the NIS from 2017 to 2020 and then served as Moon's national security adviser for two years. (Yonhap)