People attend a rally asking for the resignation of South Korean President Park Geun-hye in Seoul, South Korea, Oct 29, 2016. Over the past week pressure has been mounting on South Korean President Park Geun-hye, who has been suspected of letting her longtime friend to intervene in state affairs. [Photo/Xinhua]

Choi, seen as a political big shot behind the curtain, has been placed behind bars since she unexpectedly returned to Seoul on Sunday after staying in Europe for about two months.

She has been suspected of pulling strings behind the scenes and interfering with government affairs by using her connection to President Park. Their friendship has lasted for about four decades.

Local media reports speculated that Choi had accessed presidential speeches and statements hours or days before President Park actually deliver them, including a landmark Dresden speech made in Germany in 2014 that laid out a vision for reunification with the Democratic People's Republic of Korea (DPRK).

Copies of presidential reports had been reportedly brought to Choi every day, including documents on presidential schedule for overseas trips and secret contacts with the DPRK under the previous Lee Myung-bak administration.

Choi also allegedly meddled in major government decisions, including the shutdown of the Kaesong Industrial Complex and the appointment of ministers. The decisions were made after consulting with Choi's own advisers, including a commercial film director and a former fencer of the national team.

Corruption allegations included Choi's attempt to privatize non-profit Mir and K-Sports Foundations, which were recently established through an unprecedentedly rapid approval by pressuring conglomerates, including Samsung and Hyundai, into donating tens of millions of U.S. dollars.

Choi has also been accused of peddling influence to enable her daughter to illicitly enter a prestigious university. It encouraged even high school students in a society where college education determines the majority part of their lives to take to streets for rallies over the weekend.