Investigators raided the office of an auto parts company headed by the family of an elder brother of former President Lee Myung-bak on Wednesday as part of a slush fund investigation involving a partner firm that the former president is suspected of owning.

Investigators from the Seoul Eastern District Prosecutors' office searched the offices and residences of people related to the parts firm IM in the city of Gyeongju, some 370 kilometers southeast of Seoul, officials said.

Officials said the raid is part of an investigation into suspicions that IM's partner firm, DAS, which is headed by the same brother of Lee, created a 12 billion-won ($11.2 million) slush fund and kept it under dozens of borrowed names. 

The former president has long been dogged by allegations that he's the real owner of DAS. Should the allegations of Lee's ownership be confirmed, Lee could be investigated over the slush fund.

Last week, a ruling Democratic Party lawmaker, Rep. Park Beom-kye, raised allegations that Lee's brother sent 900 million won to IM, which is headed by his son, between 2009 and 2010 in an attempt to evade gift tax associated with giving money to his son.

Park also claimed that Lee's brother is believed to have established IM for his son. That, in turn, shows that the brother is not the real owner of DAS because, had he been its real owner, he would have just handed control of the company to the son, rather than creating a new company, Park claimed.

DAS also was one of the biggest investors in the investment firm BBK, which was founded by Korean-American businessman Kim Kyoung-joon and has been accused of rigging the stock price of a BBK subsidiary and pocketing millions of dollars in ill-gotten profits.

Ahead of the 2007 presidential election, Lee was accused of being the real owner of BBK and DAS, and therefore responsible for the share price rigging. Prosecutors at the time looked into the allegations and found no evidence backing those suspicions.(Yonhap)