According to the sources, Lee Pal-seung, who headed Woori Finance Holdings from 2008 to 2013, told prosecutors he handed over

2.25 billion won (US$2.1 million) to Lee's son-in-law in 2007.

Prosecutors suspect that about 500 million won of that money was delivered to the 71-year-old Kim via Lee's elder brother.

Kim is also suspected of using a corporate credit card of auto parts manufacturer DAS to buy about 400 million won worth of goods from department stores and duty-free shops from the mid-1990s to 2007.

DAS is at the center of Lee's scandal as he is suspected of being its secret owner. The former president has stubbornly insisted that DAS belongs to his eldest brother.

Prosecutors say Kim's usage of a DAS credit card, if confirmed, can constitute an act of embezzlement, as she had nothing to do with the company.

Kim is also suspected of involvement in the National Intelligence Service's secret payment of $100,000 to the presidential office Cheong Wa Dae in 2011, as a former presidential secretary confessed that he delivered the off-book fund to one of Kim's aides.

Lee, who was president from 2008 to 2013, reportedly denied all charges related to him and his wife during a 21-hour questioning at the Seoul Central District Prosecutors' Office earlier this week.

During the interrogation, the 77-year-old Lee acknowledged having taken the NIS fund but refused to explain where he spent it, while prosecutors have suspected Kim used the money personally.

In the face of denials by Lee, prosecutors are carefully examining the necessity, timing and methods of questioning Kim, the sources said.

They said any decision to question Kim will be made after prosecutors make a decision on whether to seek a warrant to arrest the former president. (Yonhap)