The corruption investigation office for high-level officials has called in key suspects for questioning over allegations that presidential and defense officials interfered in a sensitive military inquiry concerning the on-duty death of a Marine last year, multiple sources said Friday.

Yoo Jae-eun, a legal affairs official at the defense ministry, and Park Kyung-hoon, a former acting chief of the Criminal Investigation Command under the defense ministry, underwent the Corruption Investigation Office for High-ranking Officials’ questioning over the young Marine’s death at the CIO in Gwacheon, Gyeonggi Province.

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 on his handling of the inquiry on the death of a young marine Cpl. Chae Su-geun. Chae died during a mission to search for civilian victims of heavy downpours last summer.

Col. Park spearheaded the preliminary probe into what contributed to the death of Chae. In a document detailing the investigation findings, the Marine investigation unit reportedly listed eight officials, including the commander of the 1st Marine Division, on suspicion of negligent homicide and other charges. Then Defense Minister Lee Jong-seop had initially approved the findings after being briefed in July last year, but later issued an order to put off the transfer to the police, citing the need for further review.

Nevertheless, Col. Park transferred the case in August last year. Col. Park's move prompted the ministry to retrieve the case back from the police to be reviewed by its Criminal Investigation Command under the ministry, while Col. Park has since been relieved of his duties by the Marine Corps for his alleged insubordination.

Yoo is suspected of talking on the phone with a presidential secretary before interfering in Park's probe. Also, Yoo allegedly called Col. Park several times asking him not to identify suspects, charges or other details in the inquiry result. Furthermore, Yoo was accused of involvement in the defense ministry's prosecution illegally retrieving inquiry findings that Col. Park's team had referred to the police, without obtaining a seizure warrant.

Park Kyung-hoon, who was in charge of reviewing the probe result as a then acting chief of the Criminal Investigation Command, is suspected of reducing the number of suspects from eight to two after receiving the case from the police. The CIO suspects that there was pressure from the top, including Lee, in the process of decreasing the number of suspects.

The CIO plans to investigate further Marine Corps Commandant Lt. Gen. Kim Kye-hwan, who is accused of ordering to hold off on the transfer of the case, on Saturday. Also, the CIO plans to investigate former Defense Minister Lee after questioning those key suspects, according to the CIO.

Meanwhile, the opposition-controlled National Assembly unilaterally passed a special bill Thursday to open an investigation into suspicions that the Yoon Suk Yeol administration abused its power to disrupt a probe into the death of the Marine last year.

On Thursday, the presidential office expressed strong regret over the passage of the controversial bill by the opposition-led National Assembly.

In a radio show on Friday, Yoon’s senior political secretary Hong Chul-ho hinted at the possibility that Yoon could veto the bill. Hong said that if the top office accepts the bill, it would set a "bad precedent" and could even be considered a "dereliction of duty."

Hong said that the ongoing investigation by the police and the CIO into the case should take priority before considering the special counsel probe, saying that it would be best to wait until the current investigation is completed. Hong added that the president should abide by the law and cannot just accept a special probe when separate legal procedures related to the case are already underway.