The state anti-corruption agency summoned a key suspect in its investigation into alleged state intervention in the case of a Marine's death probe during a rain search and rescue operation last year.

The Corruption Investigation Office for High-ranking Officials(CIO) questioned Yoo Jae-eun, the defense ministry's general counsel, for around 14 hours on Friday, on charges of power abuse and obstruction of exercise of one's right.

Yoo is suspected of playing a role in retrieving from the police an initial report from a Marine probe into the death, and reducing the number of key suspects in the case.

Following the interrogation, Yoo declined to comment when reporters asked whether she admits to the charges, or had committed perjury while testifying at the National Assembly.

This is the CIO's first official interrogation of a suspect in the case, after the agency conducted an informal questioning of former defense minister Lee Jong-sup last month.