Prosecutors immediately began questioning ex-Ssangbangwool Group Chairman Kim Seong-tae upon arriving from Thailand, in connection with the prosecution's ongoing investigation into allegations of corruption against main opposition leader Lee Jae-myung.

Kim, who was arrested by investigators from the state agency after boarding a flight in Bangkok some eight months after fleeing South Korea, was seen entering the Suwon District Prosecutors' Office in Gyeonggi Province in an escort vehicle.

The voluntary return comes a week after he was apprehended by Thai police at a golf club near Bangkok, after which he was about to stand trial for illegally staying in the country.

Kim is a key suspect in several high-profile corruption investigations, including embezzlement, payment of main opposition Democratic Party(DP) chief Lee Jae-myung's legal fees by proxy and the transfer of cash remittance to North Korea. 

The prosecution plans to continue its probe through Wednesday before requesting a court warrant for Kim's arrest.