Inchon prosecutors office has been investigating alleged corruption of the ship owner, Yoo Byung-eon, and his family members.
Cheonghaejin Marine, the operator of the ferry Sewol which capsized near Jindo island off the countrys southwest coast on April 16, has been under suspicion that it had illegally modified the ferry to expand passenger cabins and overloaded cargo.
Investigators raided some 10 places, including companies and religious communities linked to Yoo, to search and seize financial documents and related data.
Yoo (73) is a former chairman of the Semo Group, which went bankrupt in 1997, according to local daily Jungang Ilbo.
Assets owned by Yoo were estimated at 560 billion won (540 million U.S. dollars). Prosecutors have been tracing bank accounts and foreign real estates owned by Yoo and his family members, including a 3.5 million dollar mansion in New York.