Investigators believe they are narrowing in on the real owner of the sunken Sewol-ho ferry,
which they believe is the key to unlocking what may have caused the accident.
Key figures associated with Chonghaejin Marine Company, the practical owner of the ferry, have not been cooperating with the investigation.
Prosecutors summoned Yoo Dae-gyun, the first son of Yoo Byung-eun, for questioning Monday morning, but he failed to appear.
If he had shown up, they would have asked him about his involvement in Semo Group, under which Chonghaejin operates.
The prosecution has issued an arrest warrant for Yoo to force him in.
Yoo currently holds majority shares in three Semo Group affiliates.
He was paid nearly 10-thousand U.S. dollars a month for his duties, and the prosecution suspects he is deeply involved with the day-to-day operations.
Investigators are also looking at him on charges of tax evasion.
Prosecutors did have a chance to talk with another member of the Yoo family on Sunday.
Yoo Byung-il, the older brother of Yoo Byung-eun, was questioned overnight on his possible involvement in the construction of the Sewol-ho ferry and the business operations of Chonghaejin Marine Company.
Yoo Byung-eun is likely to be summoned sometime this week.
While investigators hone in on the ferry operator and owner, the search for those still missing continues off Jindo island in southwestern Korea.
Fast tidal currents have made it difficult for rescue personnel to find the 29 passengers still unaccounted for.
Operations are focused on the third and fourth floor of the vessel, but with the threat of the fourth floor collapsing, authorities say divers are looking for a new way inside, by breaking through the walls of the vessel.
Connie Kim, Arirang News.