Story highlights Authorities say 169 people are dead; 133 still missing

Owner is known as the "millionaire with no face," as he rarely appears in public

Hopes are fading for survivors with news that divers haven't found any air pockets

Devastated high school set to resume classes Thursday

South Korean authorities searched the offices of the company that owns the sunken ferry Sewol on Wednesday, prosecutors confirmed to CNN, broadening a criminal investigation that has already ensnared 11 members of the ill-fated ship's crew.

Investigators also searched the offices of 20 organizations affiliated with Cheonghaejin Marine Co. as well as the home of Yoo Byung-eun, a billionaire whose family appears to control the company, according to the semiofficial Yonhap News Agency.

Yoo is known in South Korea as the "millionaire with no face" because he rarely appears in public. According to major South Korean newspapers, he also has an artistic alter ego -- Ahae -- as a photographer who has won international acclaim.

His website appears to show Yoo taking pictures, but his face is not visible.

Through an investment vehicle and subsidiary, Yoo and his two sons control the shipping company that operated the ferry. Korean tax authorities say that under the family's ownership, the ferry company has been struggling and reported a loss last year.

Days after the ferry sank, the company sent out its president to apologize, but not Yoo -- who's had a brush with bad publicity before.

In 1987, more than 30 people from a religious group were found dead, bound and gagged in a factory outside of Seoul. Officials investigated the incident as a mass murder-suicide, and also investigated whether Yoo had any connection to the event, but determined he wasn't involved.

Prosecutors in the South Korean city of Busan are also investigating the private organization responsible for inspecting and certifying ships for the South Korean government, Yonhap reported.

Investigators are looking for any evidence of possible wrongdoing in relation to the Korean Register of Shipping's safety inspection of the Sewol, the news agency reported, citing an unnamed prosecutor.

The Sewol sank April 16 during a routine trip from Incheon to the resort island of Jeju . Among its 476 passengers and crew were more than 300 high school students on a field trip.

Authorities said Thursday the death toll had climbed to 169, leaving 133 people still missing.

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Photos: Photos: South Korean ferry sinks – A relative of a victim weeps as she and others stand on the deck of a boat during a visit to the site of the sunken Sewol ferry on April 15, 2015 -- one day before the one year anniversary of the disaster. Hide Caption 1 of 55 Photos: South Korean ferry sinks – A relative hands out flowers to others on the deck of a boat during a visit to the site of the sunken ferry. More than 100 relatives of victims of South Korea's Sewol ferry disaster tearfully cast flowers into the sea. Hide Caption 2 of 55 Photos: South Korean ferry sinks – A man hold a flower as he stands on the deck of a boat during a visit to the site of the sunken Sewol ferry, off the coast of South Korea's southern island of Jindo. Hide Caption 3 of 55 Photos: South Korean ferry sinks – The mother of Sewol ferry disaster victim, Danwon High School student Lim Kyung-Bin, attends a rally to pay tribute to the victims of the ferry disaster on April 11, 2015, Seoul, South Korea. Hide Caption 4 of 55 Photos: South Korean ferry sinks – Relatives of victims of the Sewol ferry disaster march across a bridge over the Han river in Seoul on April 5, 2015. More than 200 people participated in the march from Ansan city. Many of them were the parents of the 250 students who died when the overloaded ferry sank off Jindo on April 16, 2014. Hide Caption 5 of 55 Photos: South Korean ferry sinks – Relatives of victims of the Sewol ferry hold portraits of victims during a rally on April 5, 2015 in Seoul. Relatives, students and citizens attended the vigil to pay tribute to the victims of the ferry disaster and demanded that the wreckage be salvaged. Hide Caption 6 of 55 Photos: South Korean ferry sinks – Sewol ferry captain Lee Joon-Seok was acquitted of murder, avoiding a death sentence, but was sentenced to 36 years in jail on November 11 for his role in the maritime disaster that killed more than 300. Hide Caption 7 of 55 Photos: South Korean ferry sinks – Shoes believed to belong to the missing and the deceased are on display at the harbor. Hide Caption 8 of 55 Photos: South Korean ferry sinks – Jindo harbor, where the search operation is based, has become a memorial for those who lost their lives. Yellow ribbons and photos are displayed as people come to pay their respects. Hide Caption 9 of 55 Photos: South Korean ferry sinks – A joint government-civilian task force is still looking for the missing, but winter is fast approaching. Hide Caption 10 of 55 Photos: South Korean ferry sinks – Ten are still missing from tragic ferry sinking last April, which killed more than 300. Six months later, families are still waiting for their loved ones to be found. The parents of 16-year-old Huh Da-yoon, pictured, are among them. Hide Caption 11 of 55 Photos: South Korean ferry sinks – The families of the ten who remain missing have been waiting in Jindo Indoor Gymnasium since the first day. Families can watch search mission in real time on a large monitor in the gym. Hide Caption 12 of 55 Photos: South Korean ferry sinks – South Korean President Park Geun-hye weeps while delivering a speech to the nation about the sunken ferry Sewol at the presidential Blue House in Seoul, South Korea, on Monday, May 19. More than 200 bodies have been found and nearly 100 people remain missing after the ferry sank April 16 off South Korea's southwest coast. Hide Caption 13 of 55 Photos: South Korean ferry sinks – Police in Seoul detain a protester during a march Saturday, May 17, for victims of the Sewol. Hide Caption 14 of 55 Photos: South Korean ferry sinks – A girl in Seoul holds a candle during a service paying tribute to the victims of the Sewol on Wednesday, April 30. Hide Caption 15 of 55 Photos: South Korean ferry sinks – People pay tribute to victims at a memorial altar in Ansan, South Korea, on Tuesday, April 29. Hide Caption 16 of 55 Photos: South Korean ferry sinks – A police officer holds an umbrella for a relative of a missing ferry passenger Monday, April 28, in Jindo, South Korea. Hide Caption 17 of 55 Photos: South Korean ferry sinks – South Korean Buddhists carry lanterns in a parade in Seoul on Saturday, April 26, to honor the memory of the dead and the safe return of the missing. Hide Caption 18 of 55 Photos: South Korean ferry sinks – Divers search for people in the waters near Jindo on April 26. Hide Caption 19 of 55 Photos: South Korean ferry sinks – People in Ansan attend a memorial for the victims on April 26. Hide Caption 20 of 55 Photos: South Korean ferry sinks – A diver jumps into the sea near the sunken ferry on Friday, April 25. Hide Caption 21 of 55 Photos: South Korean ferry sinks – A relative of a passenger weeps while waiting for news of his missing loved one at a port in Jindo on April 25. Hide Caption 22 of 55 Photos: South Korean ferry sinks – People attend a memorial for the victims at the Olympic Memorial Hall in Ansan on Thursday, April 24. Hide Caption 23 of 55 Photos: South Korean ferry sinks – Yellow ribbons honoring the victims flap in the wind as a hearse carrying a victim's body leaves Danwon High School in Ansan on April 24. Most of the people on board the ferry were high school students on their way to the resort island of Jeju. Hide Caption 24 of 55 Photos: South Korean ferry sinks – People attend a memorial for the victims at Olympic Memorial Hall in Ansan. Hide Caption 25 of 55 Photos: South Korean ferry sinks – Search personnel dive into the sea on Wednesday, April 23. Hide Caption 26 of 55 Photos: South Korean ferry sinks – Flares light up the search area on Tuesday, April 22. Hide Caption 27 of 55 Photos: South Korean ferry sinks – The sun sets over the site of the sunken ferry on April 22. Hide Caption 28 of 55 Photos: South Korean ferry sinks – A relative of a ferry passenger prays as she waits for news in Jindo on April 22. Hide Caption 29 of 55 Photos: South Korean ferry sinks – The search for victims continues April 22 in the waters of the Yellow Sea. Hide Caption 30 of 55 Photos: South Korean ferry sinks – Rescue workers in Jindo carry the body of a passenger on Monday, April 21. Hide Caption 31 of 55 Photos: South Korean ferry sinks – Divers jump into the water on April 21 to search for passengers near the buoys that mark the site of the sunken ferry. Hide Caption 32 of 55 Photos: South Korean ferry sinks – Search operations continue as flares illuminate the scene near Jindo on Sunday, April 20. Hide Caption 33 of 55 Photos: South Korean ferry sinks – Relatives of missing passengers grieve April 20 in Jindo. Hide Caption 34 of 55 Photos: South Korean ferry sinks – Relatives of passengers look out at the sea from Jindo on April 20. Hide Caption 35 of 55 Photos: South Korean ferry sinks – Police officers in Jindo stand guard Saturday, April 19, to prevent relatives of the ferry's missing passengers from jumping in the water. Some relatives said they will swim to the shipwreck site and find their missing family members by themselves. Hide Caption 36 of 55 Photos: South Korean ferry sinks – Family members of missing passengers hug as they await news of their missing relatives at Jindo Gymnasium on April 19. Hide Caption 37 of 55 Photos: South Korean ferry sinks – South Korean Navy Ship Salvage Unit members prepare to salvage the sunken ferry and search for missing people on April 19. Hide Caption 38 of 55 Photos: South Korean ferry sinks – Lee Joon Suk, the captain of the Sewol, is escorted to the court that issued his arrest warrant Friday, April 18, in Mokpo, South Korea. Hide Caption 39 of 55 Photos: South Korean ferry sinks – A woman cries as she waits for news on missing passengers April 18 in Jindo. Hide Caption 40 of 55 Photos: South Korean ferry sinks – A searchlight illuminates the capsized ferry on Thursday, April 17. Hide Caption 41 of 55 Photos: South Korean ferry sinks – A woman cries during a candlelight vigil at Danwon High School in Ansan, South Korea, on April 17. Hide Caption 42 of 55 Photos: South Korean ferry sinks – Family members of passengers aboard the sunken ferry gather at a gymnasium in Jindo on April 17. Hide Caption 43 of 55 Photos: South Korean ferry sinks – The body of a victim is moved at a hospital in Mokpo on April 17. Hide Caption 44 of 55 Photos: South Korean ferry sinks – Relatives of a passenger cry at a port in Jindo on April 17 as they wait for news on the rescue operation. Hide Caption 45 of 55 Photos: South Korean ferry sinks – South Korean coast guard members and rescue teams search for passengers at the site of the sunken ferry on April 17. Hide Caption 46 of 55 Photos: South Korean ferry sinks – A relative of a passenger cries as she waits for news on Wednesday, April 16. Hide Caption 47 of 55 Photos: South Korean ferry sinks – Relatives check a list of survivors April 16 in Jindo. Hide Caption 48 of 55 Photos: South Korean ferry sinks – Rescue crews attempt to save passengers from the ferry on April 16. Hide Caption 49 of 55 Photos: South Korean ferry sinks – A relative waits for a missing loved one at the port in Jindo. Hide Caption 50 of 55 Photos: South Korean ferry sinks – Parents at Danwon High School search for names of their children among the list of survivors. Ansan is a suburb of Seoul, the South Korean capital. Hide Caption 51 of 55 Photos: South Korean ferry sinks – Helicopters hover over the ferry as rescue operations continue April 16. Hide Caption 52 of 55 Photos: South Korean ferry sinks – Officials escort rescued passengers April 16 in Jindo. Hide Caption 53 of 55 Photos: South Korean ferry sinks – A passenger is helped onto a rescue boat on April 16. Hide Caption 54 of 55 Photos: South Korean ferry sinks – A passenger is rescued from the sinking ship on April 16. Hide Caption 55 of 55

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South Korean ferry rescue operation

Eleven members of the Sewol's crew, including its captain, have been arrested in connection with the disaster.

Capt. Lee Joon-seok and some other crew members have been criticized for failing to evacuate the sinking ship quickly and for giving orders for passengers to remain where they were. Lee has said he was worried about the cold water, strong currents and lack of rescue vessels.

Lee and others have also drawn public anger for leaving the ship while many passengers remained on board.

Authorities still do not know precisely what caused the incident. It did not appear that the ship was overloaded, according to figures provided by the company and the South Korean coast guard. But coast guard officials said investigators won't know for sure how much cargo the ship was carrying until it is salvaged.

Hopes fading

South Korean officials continue to call their operation a search-and-rescue mission, but hopes are fading that survivors may yet be found.

Some 700 divers are participating in the search, according to Ko Myung-suk, a spokesman for the joint task force coordinating the effort. He said 36 fishing boats were positioned around the area to prevent bodies being carried away by currents.

Rescue officials said Wednesday that divers have yet to find an air pocket on the third or fourth decks, where most of the passenger bedrooms and the ship's cafeteria are located.

Rescuers haven't found a single survivor since 174 people were rescued the day the ship sank one week ago.

Many of the bodies pulled from the ferry have come from bedrooms on the capsized ship's fourth deck, said Ko.

Divers had expected to find passengers inside the third-floor cafeteria but failed to find any, the South Korean coast guard said.

While divers still have many rooms to search, no air pockets have been found on either deck, authorities said.

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Students remembered

Grief over the sinking has spread across the Korean Peninsula. Even South Korea's nemesis, North Korea, sent condolences Wednesday.

More than two-thirds of those on board the ferry were students from Danwon High School in Ansan, an hour's drive south of Seoul.

On Wednesday, some of their faces stared out from photos amid a huge bank of white flowers at a basketball area in Ansan that has been converted into a temporary memorial.

A permanent memorial is being planned for a park in Ansan.

Hundreds of people filed through the memorial Wednesday, passing about 50 large wreaths on their way to the wall of flowers and pictures.

Somber music played as visitors, including friends and relatives, passed quietly among the tributes. Some wept.

One man, from Seoul, has no ties to the school but came to grieve for the young lives lost.

"I have a daughter," the man told CNN's Nic Robertson. "I think of her alone in black waters. It's just so terrible. I'm angry that I couldn't do anything. So helpless."

The disaster has taken a devastating toll on the high school, where classes are due to resume Thursday.

The school is missing most of its sophomores and a vice principal who was rescued from the ferry but found dead two days after the sinking. He'd apparently hanged himself from a tree.

Lee Seung-min, 17, said one of her closest girlfriends is among the missing. She said she still holds out hope that her friend will return despite the increasingly slim chances of finding survivors.

Before the field trip, the two girls had talked about what universities they might attend, she said.