A local businessman close to a son of former President Chun Doo-hwan has undergone prosecution questioning over his suspected role in helping Chun's family manage massive slush funds, prosecution sources said Thursday.

The recent summons of Ryu Chang-hee, known as a long-time business partner of Chun's second son Jae-yong, is part of the prosecution's extensive search for unpaid fines of some 167.2 billion won (US$149.3 million) levied on the former president for amassing large ill-gotten money during his presidency in the 1980s.

In 1997, a local court ordered him to return to the state coffers the 220 billion won he was found to have illegally accumulated during his term. But he has so far paid only a quarter of the total, while refusing to pay the remainder as he was "nearly penniless."

According to the sources, a task force of the Seoul Central District Prosecutors' Office has recently summoned Ryu to look into his relations with the Chun family and his role in managing Chun's secret funds. Other details were not available. 

The businessman briefly ran the local security company named Ware Vally in 2003 set up by Chun's second son some two years before. He then handed it over to the current head, named Son Sam-soo who served as a presidential secretary under the Chun administration and has been one of his close aides.

Earlier this week, the investigators raided two offices of the company and secured relevant data. They suspect that part of Chun's fund was used in setting up the firm or it helped Chun's family launder the ill-gotten money.

During the prosecution probe in 2004 into the young Chun's tax evasion case, Ryu said Jae-yong invested some 1.7 billion won in Ware Valley after selling bonds inherited from his father.

Currently, Jae-yong's two sons each hold 7 percent of the data security company.

The 49-year-old Ryu also served as a director of BL Asset, a local property company owned by Chun's second son, with Ryu's father leading the firm from 2001 to 2006.

The older Ryu was also found to lend his name to Chun's family members for their real estate purchases, according to the 2004 probe results, and Ryu's elder sister was a member of the management of Jae-yong's medical device company.

"Ryu and his family members are suspected of being deeply involved in Chun's secret funds. Investigators are analyzing what he said during the summons along with data it secured through raids of Ryu's residency last month and the security firm," a prosecution source said.

There has been a public outcry about a delay in collecting the former president's unpaid fines as the statute of limitations in Chun's case is to expire in October.

In May, the prosecution formed a task force and vowed to mobilize all possible means to collect the remaining fine from the former president. Last month, the parliament passed a bill aimed at extending the statute of limitations on forfeiting and imposing fines on public officials' illegal wealth from three years to 10.

Under the revision, Chun is required to pay the remainder of his fines by October 2020. (Yonhap News)