SEOUL (Reuters) - Samsung Group [SAGR.UL] chief Jay Y. Lee was questioned by South Korea’s special prosecutor for more than 15 hours as part of an investigation into a graft scandal that threatens to topple President Park Geun-hye.

The 48-year-old executive, the third-generation leader of the country’s top conglomerate, made no comment as he was shown on live television leaving the prosecutor’s office in southern Seoul in a black car early on Tuesday.

Lee, who has denied allegations of bribery through Samsung Group spokespeople, had arrived at the office on Monday morning.

South Korea’s special prosecutor has focused on Samsung Group’s relationship with Park, accusing Lee in his capacity as Samsung chief of pledging 43 billion won to a business and organizations backed by Park’s friend, Choi Soon-sil, in exchange for support of a 2015 merger of two Samsung companies.

Proving illicit dealings between Park or those linked to her and Samsung Group is critical for the special prosecutor’s case that ultimately targets Park, analysts have said.

The prosecution has also identified four other Samsung executives as suspects and have summoned three of them.

Samsung Group President Chang Choon-ki was questioned on Sunday and Samsung Electronics 005930.KS President Park Sang-jin and another executive were quizzed on Monday.

Park, Choi, and Samsung Group [SAGR.UL] have denied bribery accusations.

Park was impeached by parliament in December and South Korea’s Constitutional Court will decide whether to uphold that decision. She has been stripped of her powers in the meantime.

Lee arrived at the prosecution office in southern Seoul early on Monday in a black sedan, dressed in a dark blue suit and tie and flanked by Samsung Group officials and his lawyer.

“I will once again tell the truth to the special prosecution,” Lee told reporters, while protesters outside the office held up signs calling for his arrest.

EXECUTIVES QUESTIONED

The special prosecution team said investigators were questioning two other Samsung executives as suspects. Both are officers of the Korea Equestrian Federation and have been questioned previously in the case.

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One of those two, Samsung Electronics Co Ltd president Park Sang-jin, did not respond to reporters on his arrival at the special prosecution team’s office.

Lee Kyu-chul, spokesman for the special prosecution office, told a news briefing the office would decide soon whether to make a second arrest warrant request for the Samsung Group chief. He did not comment on other details, including what Jay Y. Lee said during questioning.

Prosecutors would also consider whether to seek arrest warrants for four other Samsung Group executives identified as suspects, the spokesman added. The prosecutor’s office had previously said it would not seek arrests for any Samsung executives other than Lee.

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In January, the special prosecutor sought a warrant to arrest Samsung chief Lee after questioning him for more than 22 hours, accusing him of paying bribes to win the state pension fund's support for the controversial merger of Samsung C&T Corp 028260.KS and Cheil Industries Inc.

However, a Seoul court rejected that request.

Chang Choong-ki, deputy head of Samsung Group’s corporate strategy office, known informally as its “control tower”, was questioned as a suspect on Sunday and returned home hours later.

Shares in Samsung Electronics were down 0.9 percent by 0600 GMT on Monday, compared with a flat wider market .KS11.

“The issue will have limited impact on share prices, except if the worst-case scenario happens, since political issues previously did not have a big influence on share prices or earnings,” said Bae Sung-young, a stock analyst at Hyundai Securities.

($1 = 1,152.5300 won)