Lee Hak-soo was questioned for 16 hours Thursday by prosecutors who are looking into a raft of corruption allegations surrounding the former leader and his family.
The sources said Lee Hak-soo confessed that Samsung paid billions of won in litigation fees on behalf of DAS in a tacit agreement with the presidential office. He headed the now-disbanded group control tower in the late 1990s and 2000s.
The prosecution plans to summon former presidential officials to question the payment that it regards as a bribery, they said.
DAS filed a suit against a U.S.-based investment advisory firm in the early 2000s, seeking to recoup its 14 billion-won ($13 million) investment. It hired a law firm, Akin Gump, in 2009 and got back the money in 2011 from the company run by the then president's alienated former business partner.
Lee was president from 2008 to 2013.
The prosecutors were probing allegations that the former president mobilized diplomats to pressure the former partner to return the money. In the course of inquiry, they found evidence that Samsung paid for DAS' fees to the law firm.
The prosecution suspects that the payment may have been made in return for a special presidential pardon in 2009 of Samsung Chairman Lee Kun-hee, who was convicted of embezzlement and other charges in a slush fund scandal.
Lee Myung-bak's aides denied such allegations. The presidential office was not involved in the lawsuit and DAS was approached by a lawyer from the law firm who offered to provide free legal service, they claimed.
DAS is also under investigation over suspicion that it created a 12 billion-won slush fund for the former president. Lee has denied the accusations. (Yonhap)