The sunken ferry Sewol lacked features for holding cargo in place, investigators said Thursday.
According to the investigation team, the Sewol was fitted with an insufficient number of cones ― structural features used to hold cargo containers in place ― and lacked turnbuckles.
Due to the lack of turnbuckles, equipment used to hold cargo in place using steel wires, the containers were only tied down with rope, which in turn caused the cargo to slide when the ship lost balance.
Also on Thursday, more than 10 locations linked to Yoo Byung-eon, de facto owner of the ferry, were raided.
In the latest raid, offices and homes of Byun Ki-choon and Hwang Ho-eun, who run companies owned by the Yoo family, were searched.
The investigators of the Incheon District Prosecutors' Office also continued to grill Yoo's closest associates.
For the second consecutive day, former Ahae Corp. CEO Lee Kang-se was questioned over suspicions of aiding Yoo in the establishment of massive slush funds.
Ahae, a paint manufacturer controlled by the Yoos, is a large sponsor of Yoo's photography career, having invested in Ahae Press France, a company established to publish Yoo's photographs.
The investigators suspect that Lee received orders regarding purchasing Yoo's works from Kim Pil-bae, one of Yoo's closest associates who served as the chief of Moonjin Media, another business under Yoo's control.
Kim, along with Yoo's son Yoo Hyeok-gi and Hankook Pharma chief Kim Hye-kyung, has been summoned to appear for questioning by Friday. The younger Yoo, however, is said to be unlikely to be able to answer the summons.
The prosecution also applied for arrest warrants for Song Kook-bin, chief of the door-to-door sales company Dapanda Co. owned by the Yoos. The prosecution suspects that Song was deeply involved in irregular transactions involving the Yoos. In addition, Song is thought to have had a hand in purchasing photographs taken by Yoo for as much as 50 million won (S$60,120) each, dealing significant damages to the company.
The search for the Sewol's missing passengers, meanwhile, progressed slowly, hampered by rapid tidal currents.
The area's notoriously rapid currents caused the authorities to withdraw the diving bell, which the rescue workers only managed to deploy in the early hours of the day.
As of 6 pm, the official death toll stood at 219 and the number of people missing at 83, according to the government response team spokesman Koh Myung-suk.
In the investigation into the cause of the ferry accident, Chonghaejin Marine Co. CEO Kim Han-sik is to be questioned again by the prosecution.
This time, Kim is to be questioned as a suspect in the developments that led to the Sewol being overloaded on the day of the accident.
Earlier in the week, Kim was grilled as a suspect in the Yoo family's alleged wrongdoings, including embezzlement and tax evasion.
With the authorities tentatively concluding that overloading was a major factor in the ship's sinking, Chonghaejin Marine officials in related positions are also facing legal consequences.
According to sources, the prosecution is seeking arrest warrants for the two Chonghaejin Marine officials taken into custody on Wednesday.
The two, identified as Ahn and Kim, are to be charged for manslaughter. Ahn is also suspected of embezzling 30 million won generated while making modifications to the ship.
The Sewol is reported to have undergone extensive modifications that raised its centre of gravity, and was kept in operation despite the management being aware that its ability to maintain balance was severely impaired.