Hope has dimmed for finding survivors among the 268 passengers missing from Wednesday’s sinking of the South Korean ferry The Sewol after the entire boat became submerged on Friday. Previously, a portion of the boat’s hull had remained above water.

Twenty-eight people are confirmed dead in the disaster, South Korea’s worst maritime transport catastrophe in decades. One hundred and seventy-nine passengers were rescued in the immediate aftermath of the tragedy.

Government rescue operations, sharply criticized by experts and victims’ family members, found no new survivors on Friday. Divers were able to cut into the ship’s hull before rough waters forced their retreat. A Coast Guard spokesman said divers would reenter the vessel as soon as possible.

Efforts have been hampered by extremely turbid water. “We cannot even see the ship’s white color. Our people are just touching the hull with their hands,” said Kim Chun-il, a diver from Undine Marine Industries.

Deepening the tragedy, one of the survivors killed himself on Friday. Kang Min Kyu, 52, was vice principal of Ansan Danwon High School, a suburban Seoul school that had sent about 350 16-and 17-year-old students on the outing aboard The Sewol. Kyu was found hanging from a tree near a gymnasium in the nearby port city of Jindo, where family members of missing passengers had been camping out.

The cause of the disaster is undetermined, but the South Korean government has moved to pin blame on the ship’s crew. The Sewol’s captain, Lee Joon Suk, 68, and two other officers were arrested early Saturday. The captain faces five charges including negligence on duty and violation of maritime law. The government has focused on the fact that Suk was not on the bridge when the ship capsized about 20 kilometers from the island of Byungpoong, off the southwestern tip of the Korean peninsula, where it was passing on its route from the northwestern port of Incheon to the island of Jeju, a popular tourist destination.

“It is not clear where [Lee Joon Suk] was when the accident occurred, although it is clear that he was not in the steering room before the actual accident happened,” state prosecutor Jae-Eok Park said Friday.

However, a retired ferry captain, Malcolm Shakesby, told the BBC it was not unusual for a ship captain to leave the bridge to an officer.

“Depending on whether or not is was in pilotage waters, then yes, the master would be expected to be on the bridge, but if it wasn’t in pilotage waters it’s a common practice for one of the officers to be doing navigation,” he said.

Suk, an experienced captain who was substituting for The Sewol’s regular skipper, issued an emotional apology on YTN network television. “I am really sorry,” he said. “I don’t know what to say. I’m sorry.”

The South Korean Ministry of Oceans and Fisheries confirmed on Thursday that the ship followed closely its approved route. However, this was seemingly contradicted by the Yellow Sea Maritime Police Agency, which said the ship deviated from its route. The South Korean government had not squared the competing reports.

An expert with the Mokpo National Maritime University, Professor Rim Gung-su, has theorized that labor cost savings played a role in the disaster.

Rim believes that ship cargo is frequently poorly secured “as operators seek to cut labor costs,” according to the Los Angeles Times. “The ship was moving at full speed; it was very foggy and there were probably a lot of fishing boats around,” Rim said. “My theory is that the captain turned suddenly to the right to avoid a boat, which could have caused the cargo to fall over, throwing The Sewol off balance.”

Rim also noted that the ship, built in Japan in 1994, was altered soon after its acquisition by Cheonghaejin Marine in 2012 so that it could carry more cargo. This could have “raised the vessel’s center of gravity, making it more vulnerable to tipping in response to a shift of weight,” the Times reports.

A transcript between The Sewol and the Ministry of Oceans and Fisheries made public appeared to substantiate Rim’s analysis. As the ship began to roll, large containers in its steerage began to topple, accelerating the capsizing. When advised to evacuate, The Sewol radioed back claiming that it was impossible for passengers to move. It seems that virtually all the survivors escaped from the ship’s upper deck, raising the possibility that escape from the lower decks was blocked.

The ship capsized in the space of two hours, during which time several attempts were made to right it. The failures came in spite of the fact that the ship was easily within the 5 percent maximum list within which righting should succeed.

The Yonhap News Agency has reported that authorities will investigate whether the vessel’s machinery was in good working order.

It is within the realm of possibility that there could be survivors who have found air pockets in the ship’s hull. Survival would then depend on the speed of the rescue. With the water temperature at 12 degrees Celsius (53 degrees Fahrenheit), hypothermia poses a serious risk to survivors.

“Absolutely, there could be areas in there where there is breathable air,” Mike Dean, deputy director for salvage and diving for the US Navy told the media. “But the trouble right now is the temperature and getting people to them.”

In another cruel twist, text messages purporting to be sent from survivors that had increased hopes among relatives have turned out to be hoaxes. Government spokesmen have threatened to prosecute those responsible for the messages.

The government has deployed three cranes to the area with the aim of raising the 6,285-ton ferry.