According to prosecutors, Cha apparently used his network to coerce a small advertising agency, which acquired POSCO's in-house ad firm Poreka, into relinquishing its shares to Cha's new company.

When Cha was trying to take over Poreka, Park apparently ordered An Chong-bum, former senior presidential secretary under arrest for his role in the scandal, to ensure Poreka wouldn't be picked up by a major corporation instead.

After his takeover attempt failed, Cha teamed up with Choi to found another ad firm, Playground Communications, with an objective of cornering the ad market for major conglomerates.

Prosecutors alleged that Park ordered An to contact telecom giant KT and tell its leadership to hire acquaintances of Cha's and Choi's as advertising executives.

With friendly faces in key positions, Playground won ad contracts for KT worth 6.8 billion won (US$5.8 million) between March and August this year, and helped Cha net some 510 million won in profits, according to prosecutors.

In addition, Cha is also suspected of having embezzled millions at another of his ad firms, Africa Pictures, to pay off personal debts and finance his child's overseas education.

Kim Jong-min, Cha's attorney, later told reporters that his client met with former presidential chief of staff Kim Ki-choon at the latter's residence.

The attorney said the meeting, which took place around June or July 2014, was arranged by Choi, and lasted for about 10 minutes.

Also present at the meeting were Kim Chong, the former vice minister of culture, sports and tourism who's been arrested in the scandal, and Chung Sung-keun, the then culture minister nominee.

In earlier interviews, Kim Ki-choon had claimed that he didn't know anything about Choi and her involvement in state affairs.

Cha's attorney also said Cha once played a round of golf with Choi and the mother-in-law of Woo Byung-woo, former presidential secretary for civil affairs under investigation for his role in the scandal.

Kim Jong-min said he wasn't aware of the exact nature of that meeting or what sort of conversations took place, but that he believed Choi had set up the round.

Meanwhile, prosecutors said Park has yet to respond to their request for face-to-face questioning. They sent the request to Park's attorney, Yoo Yeong-ha, last Wednesday.

Park, recently dubbed by prosecutors as a key suspect in the scandal, is alleged to have directly or indirectly pressured major conglomerates into making donations to Choi's foundations, which legal experts say could constitute an abuse of authority. (Yonhap)