Investigators are looking into possible irregularities in a real estate transaction with the children of former National Intelligence Service chief Won Sei-hoon, local media reported Sunday.

According to news reports citing unnamed prosecution officials, investigators looking into allegations surrounding Won have secured evidence of suspicious developments in a real estate purchase made by one or more of his children. Won, who is suspected of a wide range of wrongdoings including interfering with local politics and wrongful use of NIS funds, has two daughters and a son. 

According to reports, Won’s children purchased an apartment located in southern Seoul sometime after Won took office as the NIS chief in 2009. The price of the apartment, over 1 billion won ($937,000) at the time, is reported to have been paid fully in cash.

The investigators have questioned the previous owner of the property, and obtained income and tax records from the National Tax Service.

The investigators believes the younger Wons were unlikely to have come by the means of making the transaction without help from Won or other parties.

In an earlier development, investigators raided the homes of Won and former NIS officials over suspicion that Won embezzled large sums from the covert operations budget allocated to the NIS chief. The chief of the spy agency is given about 4 billion won each year to fund intelligence activities.

It has also been alleged that Won confessed to handing over 200 million won to aides of former President Lee Myung-bak, implicating Lee in the expanding investigation into alleged misuse of NIS funds.

The investigation was launched after the NIS reform committee alleged that NIS funds were funneled into Cheong Wa Dae during former President Park Geun-hye’s term. The investigation has since led to the arrest of former NIS chiefs Nam Jae-joon and Lee Byung-ki.

Lee Myung-bak rejects the allegations as groundless and has accused the Moon Jae-in administration of political revenge. Two of his former aides -- Kim Jin-mo and Kim Paik-joon -- were arrested in connection with the case.

Having served as an aide for Lee Myung-bak for over 40 years, Kim Paik-joon has sometimes been referred to as the former president’s butler. He served as senior secretary for administrative affairs to Lee between 2008 and 2012. Kim Jin-mo served as a civil affairs secretary from 2009 to 2011.

Kim Paik-joon is accused of receiving 400 million won in total from the NIS in 2008 and 2010, according to prosecutors.

By Choi He-suk (cheesuk@heraldcorp.com)