The de facto head of South Korea’s enormous Samsung conglomerate was questioned for a marathon 22 hours as a suspect in a widening bribery scandal that has already seen the country’s president suspended from duty.

The prosecutors’ allegations against Lee Jae-yong, arguably South Korea’s most powerful man, show that there is no end in sight to the sensational corruption and influence-peddling scandal that has brought South Korea to a political halt.

“I deeply apologize to the people for failing to show a positive image because of this incident,” Lee said as he arrived at the prosecutors’ office in Seoul on Thursday morning. He is officially vice chairman but has been running the conglomerate since his father had a heart attack almost three years ago.

Protesters waited outside, accusing him of being the president’s accomplice and shouting “Arrest Lee Jae-yong!”

Local television showed Lee leaving the prosecutors’ office about 7:30 Friday morning, almost a full day after he arrived.

Lee Jae-yong, vice chairman of Samsung Electronics, arrives on Thursday to be questioned as a suspect in a corruption scandal that led to the impeachment of President Park Geun-Hye in Seoul. (Ahn Young-Joon/AFP/Getty Images)

Lee, 48, was questioned behind closed doors over suspicions that Samsung gave money to Choi Soon-sil, a confidante of President Park Geun-hye, in return for favorable treatment.

Choi, who held no official position but appears to have had enormous influence over the president, is on trial for bribery, coercion and abuse of power.

Park was suspended last month when the National Assembly voted overwhelmingly to impeach her. The Constitutional Court has expedited hearings on whether to uphold the impeachment and has six months to decide, but analysts say a decision could come as soon as February or March.

[ South Korea parliament votes to impeach president over corruption scandal ]

With expectations that Park will be impeached, potential presidential candidates are now jockeying for position. Ban Ki-moon, who has just finished his term as secretary-general of the United Nations, arrived back in South Korea on Thursday to great fanfare.

He is expected to run for president, although he also finds himself involved, if tangentially, in a different corruption scandal. U.S. prosecutors have charged Ban’s brother and nephew with bribery related to a skyscraper complex they owned in Vietnam. Ban has denied any knowledge of the deal.

In the corruption case centered on Park, the chiefs of South Korea’s biggest conglomerates had already been called before the National Assembly for questioning and the offices of some, including Samsung, had been raided by prosecutors looking for evidence of wrongdoing.

But the questioning of Lee on Thursday underscored how deeply mired in the scandal the conglomerates are.

Samsung is suspected of having agreed to an $18 million contract with a consulting firm owned by Choi and based in Germany, considered a front for funding Choi’s daughter’s equestrian training there. Lee has previously admitted that Samsung gave a $900,000 horse to Choi’s daughter.

For her part of the deal, Choi is accused of leaning on the National Pension Service, the world’s third-largest pension fund and a major shareholder in key Samsung units, to support an $8 billion merger between two Samsung companies. The merger helped the Lee family strengthen its grip on the conglomerate and was opposed by some international investors.

[ For South Korea’s Samsung, 2016 was an explosive year. Literally. ]

Moon Hyung-pyo, head of the National Pension Service, was arrested in December over his role in the deal, although it took place before he had started at the fund.

Samsung also donated almost $20 million to two foundations set up by Choi, which she apparently used for her own purposes.

Lee has strongly denied any bribery, telling the parliamentary panel last month that Samsung never expected anything in return for the money, which was supposed to go toward promoting South Korean culture and sports abroad.

Lee has also denied having discussed the merger or Samsung’s support for Choi’s foundations during one-on-one meetings with Park in 2015.

But fueling suspicions, an independent counsel team that is also investigating the allegations in parallel with the prosecution has obtained a Samsung Galaxy tablet that was used by Choi from July 25, 2015 — the same date that Lee and Park met, and a week before the tablet was released to the public.

The tablet contained emails between Choi and a high-ranking official at Samsung, according to the counsel’s spokesman.

As a result, the independent counsel asked the parliamentary panel to file a formal complaint against Lee for committing perjury so that it could open an investigation into whether the Samsung scion lied about the conversations.

[ Scandal shows that ‘Korean disease’ of corruption is far from cured ]

The outcome of this case could have a huge impact on Samsung, already in something of a power vacuum because Lee’s father officially remains chairman, even though he has been in a coma since May 2014.

“If Lee and other high-ranking officials at Samsung are indicted, it would definitely hinder Samsung from making important decisions like large-scale investments or mergers and acquisitions at least until the end of this year,” said Kim Sang-jo, an economics professor at Hansung University and an expert on the conglomerates.

The investigation is expected to take about eight months to resolve, but analysts are already talking about Lee’s likely arrest.

Samsung has declined to comment on Lee’s questioning.

The development is another blow for the South Korean conglomerate, coming on the heels of its embarrassing recall of the Galaxy Note 7, which had a habit of catching fire.

“Samsung’s global brand and its global businesses will be inevitably damaged by this case,” Kim said.

anna.fifield@washpost.com

Yoonjung Seo in Seoul contributed to this report.

Read more:

South Korean court to begin considering President Park Geun-hye’s impeachment

In South Korea, Samsung prepares to crown third-generation ‘emperor’

As the South Korean assembly prepares to impeach the president, paralysis looms

Today’s coverage from Post correspondents around the world

Like Washington Post World on Facebook and stay updated on foreign news