Ex-president Chun Doo-hwan's closest aide and former intelligence chief has been probed over the wealth the former leader illegally accumulated during his rule in the 1980s, prosecution sources close to the investigation said Monday.

Chang Se-dong was questioned last Tuesday over suspicions that he actively helped his former boss create a slush fund and received some of the money as a reward while serving as the head of the Agency for the National Security Planning, which later became the National Intelligence Service (NIS).

Prosecutors have grilled some of Chun's former officials, including Chang, for their possible roles in the creation of the slush fund.

In 1997, Chun was ordered by the Supreme Court to return to state coffers around 220 billion won (US$196.8 million) he illegally accumulated in bribes while in office from 1980-88. Chun has yet to pay back a large sum of the fines.

The prosecution has begun reclaiming Chun's ill-gotten gains after his family pledged early last month to return to the state 170.3 billion won worth of real estate, artwork and others to pay off the remainder of a huge amount of unpaid fines imposed on the former president.

"We understand prosecutors are investigating the former officials to learn if the former officials lent their names to help Chun hide his money and other facts," a prosecution source said.

Prosecutors said they will continue tracking the former president's slush fund based on testimonies by others while concurrently mulling criminal charges for any wrongdoings discovered in the process. (Yonhap News)