Telling reporters that she "deserves death", the woman at the centre of a scandal roiling South Korea met prosecutors examining whether she used her close ties to President Park Geun Hye to pull government strings from the shadows and amass an illicit fortune.
"Please, forgive me," Choi Soon Sil, a cult leader's daughter with a decades-long connection to Park, said through tears inside the Seoul prosecutor's building, according to Yonhap news agency.
Using a common expression of deep repentance, she added, "I committed a sin that deserves death."
Yonhap and other South Korean media later reported that Choi had been detained. Worried that Choi may be a flight risk and could destroy evidence, prosecutors placed her under emergency detention without a warrant and she was later arrested.
Other protesters screamed, "Arrest Choi Soon Sil" and "Park Geun Hye should resign".Choi, wearing a hat and a scarf, her hand pressed to her mouth, was nearly knocked off her feet several times earlier in the day as she tried to walk through a huge crowd of 300 journalists, as well as protesters and security, surrounding the building's entrance. YTN TV said that Choi, 60, lost her shoe as the throng converged on her, and a protester reportedly tried to enter the building with a bucket full of animal faeces.
The scandal exploded last week when, after weeks of speculation, Park acknowledged that Choi had edited some of her speeches and provided public relations help.
Widespread media reports say Choi, who has no official ties to the Administration, may have had a major role in government affairs.
Choi has previously said she helped Park but didn't know if she was seeing confidential information.
Investigators are trying to determine the scope of access Choi had and whether she was given sensitive presidential documents. They have raided the homes of some officials in the presidential Blue House as part of the investigation.
Park has fired some of her closest aides to try to contain the fallout. Some lawmakers and the public have called for Park's resignation or impeachment, and thousands of people have protested in the streets.
It's not clear how much influence Choi had. But many South Koreans believe there is much more to the story than Park has acknowledged, and the frenzy surrounding the scandal threatens her presidency.
Choi returned home on Sunday from seclusion in Germany. It was unclear whether there would be any details revealed from her questioning, or how long she would be in the prosecutor's office. The questioning of Choi's former associates, including a purported former employee of a host bar, lasted two days.
Choi has been close to Park since Choi's father, the leader of a religious cult, gained Park's trust by reportedly convincing her that he could communicate with her assassinated mother. Choi's father denied this in a 1990 media interview.
The senior government official who later shot and killed Park's dictator father, President Park Chung Hee, is said to have claimed that he staged his attack in part because Park Chung Hee wouldn't keep Choi's father away from the young Park Geun Hye.
Elected in 2012, Park has long been criticised for an aloof manner and for relying on only a few longtime confidantes. Most South Koreans, however, assumed those confidantes were in the Government.
That she may have been outsourcing decisions to someone outside of Government, and someone connected with a murky, lurid backstory, has incensed many.
Media reports said the younger Choi used her connections to Park to pressure businesses to give money to two nonprofit organisations Choi controlled; Choi then allegedly used some of the organisations' official funds for personal purposes.
South Korean media speculated that the two foundations collected about 80 billion won ($97.6 million) in donations from business groups in just a few months.
The president of Ewha Woman's University has resigned amid protests over allegations that Choi used her connections to Park to get her daughter into the elite school and then secure special academic treatment.
Political and business corruption remains widespread in South Korea, which has had full democracy only since the late 1980s, when it shook off decades of military dictatorship. But the current scandal has struck a chord in a way that previous ones have not.
Part of it has to do with Park Geun Hye and her past, which is deeply entwined with South Korea's recent, tumultuous history.
The legacy of her father is still divisive. Supporters see him as saving South Korea from poverty and irrelevance by building up the economy from the rubble of the Korean War.
Opponents say that the economic development came at the expense of massive human rights abuse, including the torture and death of dissidents.
