Upon Ko's request, one of the official's superiors was promoted to the position of office chief in January last year, according to prosecutors. They suspect Ko may have asked Choi to pull strings through her ties to Park.

The 41-year-old is also accused of failing to pay back 80 million won in money he borrowed from an unidentified person for stock investment, and of co-running an illegal online gambling site after gathering 200 million won from individual investors.

Ko played a key role in revealing the controversial ties between Park and Choi last year, which eventually led to the former president's dismissal in March. He claimed that Choi received and edited the president's speeches in advance despite having no policy experience or an official post in the Park administration.

While Ko was praised by some as a whistleblower, others raised suspicions that he made the revelations to gain control of a company owned by Choi.

He is known to have made some clothing items and bags for Park. (Yonhap)