Yoo Jae-eun, a legal affairs official at the defense ministry, appears at the Corruption Investigation Office for High-ranking Officials (CIO) in Gwacheon, Gyeonggi Province, April 26. Yonhap

The anti-corruption investigation office called in a key suspect for questioning Friday as part of an investigation into allegations that presidential and defense officials had interfered in a sensitive military inquiry concerning the on-duty death of a Marine last year.

Yoo Jae-eun, a legal affairs official at the defense ministry, appeared at the Corruption Investigation Office for High-ranking Officials (CIO) in Gwacheon, south of Seoul, with a lawyer to face questioning.

The probe was launched after the Marines' former top investigator, Col. Park Jung-hun, lodged a complaint against Yoo and another defense ministry official last year, accusing them of exerting undue influence in his handling of the inquiry involving a young Marine who died during a mission to search for civilian victims of heavy downpours last summer.

While the inquiry was under way, Yoo allegedly called Park several times asking him not to identify suspects, charges or other details in the inquiry result.

She was also accused of involvement in the defense ministry's prosecution illegally retrieving inquiry findings that Park's team had referred to the police, without obtaining a seizure warrant.

Park spearheaded the inquiry into what had contributed to the conscript's tragic death and who were responsible amid criticism that the search mission proceeded despite apparent safety risks and without proper safety gear.

The CIO has reportedly secured records of phone calls Yoo held with Lee Shi-won, presidential secretary for public discipline, on the day the inquiry findings were retrieved from the police.

Lee Jong-sup, who served as defense minister at that time, later said that he was informed of the retrieval after it took place, sparking suspicions that Yoo may have acted upon orders from higher levels, possibly including the presidential office.

The defense ministry maintains that no undue pressure has been exerted and the retrieval was in response to Park disobeying an order to hold off the inquiry findings.

After questioning Yoo, the CIO is expected to summon higher-ranking former ministry officials, including Lee. (Yonhap)