Worried that she might be a flight risk or destroy evidence, investigators held Choi Soon-sil, known by many in the country as the “shaman adviser” to Ms Park, amid allegations of influence-peddling and corruption at the highest levels of governance.
Ms Choi returned to Seoul from Germany over the weekend amid an escalating furore over claims that she had exerted control over the president on issues from key policy decisions to what clothes and accessories the president should wear. Allegations are also swirling that Ms Choi used her relationship with Ms Park to press top Korean companies into donating tens of millions of dollars to foundations she controls and that her daughter received preferential admission to a top university.
Ms Choi previously denied the claims, but seemed to make a confession upon arriving at the prosecutor's office on Monday.
“I have committed an unpardonable crime,” she told the jostling crowds — a statement that her lawyer quickly denied was an admission of guilt.
The frequency of corruption cases in the north-east Asian nation has made them an almost customary affair. Yet this episode stands apart for its mystical overtones. Ms Choi entered the world of high politics through her father, Choi Tae-min, a shadowy religious figure linked to cult activities.
The elder Choi became a mentor to Ms Park, whose father was president of South Korea from 1963 to 1979, after convincing her he could communicate with her late mother, who was assassinated in 1974. His hold over her earned him a Rasputin-like reputation. A leaked diplomatic cable from 2007 cited a US embassy official as saying: “Rumours are rife that the late pastor had complete control over Park’s body and soul during her formative years and that his children accumulated enormous wealth as a result.”
Following her father’s death in 1994, Choi Soon-sil filled the void as a friend and confidante to Ms Park.
The scandal has enraged many South Koreans, thousands of whom have taken to the streets to demand that Ms Park step down. Further rallies are planned this week.
On Tuesday morning a protester was detained after driving a construction vehicle into the office of the investigating officials. Ms Choi’s description of an “unpardonable crime” can be literally translated as a “sin that deserves death”, and the 60-year-old man had left his home 360km away at 3am and driven to the South Korean capital to “help Choi Soon-sil die”, local media reported him as saying.
Prosecutors over the weekend attempted to raid the presidential office — known as the Blue House — but were denied entry on the grounds of national security. Instead, investigators are being fed a slow drip of the requested documents.
Ms Park on Sunday accepted the resignation of several aides who had faced accusations of either helping or tolerating Ms Choi’s meddling in the affairs of state, as the president grappled with fallout from the scandal.
Last week local media revealed Ms Choi had been given access to confidential policy documents, including first drafts of important speeches and budget proposals. The saga has caused Ms Park’s approval ratings to plunge to record lows. A survey last week found that 40 per cent of South Koreans wanted the president to resign.
Additional reporting by Kang Buseong and Song Jung-a