South Korea's ousted president Park Geun-Hye was interrogated for 14 hours Tuesday about the corruption and abuse of power scandal that brought her down, Yonhap news agency reported.
Park denied all charges during the questioning that ended shortly before midnight, Yonhap said citing sources, adding that prosecutors declined to confirm this.
The nation's first female president, whose dismissal was confirmed by South Korea's top court earlier this month, was expected to leave the prosecutors' office after reviewing her statements made to investigators, Yonhap said.
Park, who was protected by executive privilege while in office, had earlier apologised to the public as she arrived at the prosecutors' office in Seoul, adding: "I will undergo the investigation sincerely."
As a private citizen once again, Park's convoy drove at walking pace through crowds of flag-waving supporters lining the street outside her home -- some of them lying on the pavement to try to block her exit before she left.
Every inch of the journey Tuesday morning was covered live on television, with cameramen trailing the vehicles in cars and on motorcycles and at fixed points along the route.
Questioning by prosecutors is a key step in South Korea's judicial process before a suspect is charged. It can last for many hours, late into the night, and can be repeated if officials deem it necessary.
Park faced two prosecutors and an investigator and was accompanied by one of her lawyers, but standard procedure bars him from interjecting, only allowing consultations during rest breaks -- which could be an issue for her.
The 65-year-old, who grew up in the presidential palace as the daughter of army-backed dictator Park Chung-Hee, had a packed lunch of seaweed rice rolls and sandwiches brought by one of her security guards, Yonhap said.
"She has been cooperating well," the agency quoted a prosecutor as saying.
The interrogators addressed her as "Madam president", he added, but in the transcript she was referred to as "suspect".
- Secret confidante -
Park faces multiple charges ranging from abuse of power and coercion to bribery. She is the fourth former South Korean leader to be probed or jailed over corruption scandals.
Two former army-backed leaders who served in the 1980s and 1990s -- Chun Doo-Hwan and Roh Tae-Woo -- served prison terms for bribery after they stepped down.
Roh Moo-Hyun, who served from 2003 to 2008, killed himself by jumping off a cliff after being probed by prosecutors over corruption allegations in 2009.
Park has been named as an accomplice to her secret confidante at the heart of the scandal, Choi Soon-Sil.
Choi allegedly used her presidential ties to force firms including Samsung, the world's biggest smartphone maker, to "donate" nearly $70 million to non-profit foundations which she allegedly used for personal gain.
Park is accused of offering governmental favours to the business tycoons who enriched Choi.
The former leader is also accused of letting Choi, who had no official title or security clearance, handle a wide range of state affairs including nomination of top officials or diplomats.
Park also allegedly forced her aides to create a "blacklist" of thousands of artists who had voiced criticism of her, in order to stop offering their projects state subsidies.
Prosecutors have accused her of pressing businesses including Hyundai and steelmaker Posco to award lucrative deals to firms or individuals linked with Choi.
The ex-president has repeatedly denied any wrongdoing and blamed her friend for abusing their friendship.
Choi is on trial at Seoul Central District Court -- a few hundred metres from the scene of Park's interrogation -- on charges including abuse of power and coercion.
Samsung heir Lee Jae-Yong has also been arrested and indicted for bribery and other offences.
Park won the 2012 presidential vote largely thanks to the popularity of her late father among the aged conservative voters who benefited from rapid economic growth under his iron-fisted rule from 1961-1979.
But the scandal sent her once-bulletproof support ratings to record lows.
An election to choose her successor will be held on May 9 with Moon Jae-In, her rival in 2012 and a former leader of the main liberal opposition Democratic Party, leading polls by large margins.