Jindo, South Korea (CNN) -- Angry relatives of missing South Korean ferry passengers cursed government and police officials Thursday for failing to do enough to save the lives of their loved ones as hopes dim of finding any survivors.
The relatives berated Fisheries Minister Lee Ju-young and two coast guard officials, accusing them of misleading the public about the operation and of wasting time.
"How can you fool us into believing you were out there trying to save our children?" one mother yelled at the officials.
Also, officials at the South Korean headquarters for the task force coordinating the search told CNN that they believe the body of a boy who reportedly made the first emergency call from the ship after it began to list sharply has been recovered. DNA tests will help officially identify the remains, officials said early Friday.
The ferry Sewol lurched on its side and capsized April 16 with 476 people aboard, including more than 300 high school students on a field trip to the resort island of Jeju.
The number of confirmed dead rose to 181 on Thursday, with 121 still missing, according to the South Korean coast guard.
Hopes of finding any survivors in the sunken ferry have all but evaporated following news that divers have found no air pockets on the third and fourth levels of the ship, where many passengers were thought to have been trapped.
Authorities do not yet know what caused the sinking, but a widening criminal investigation has ensnared the ship's captain and 14 other crew members and led prosecutors to search the offices of the company that owns the ship.
Authorities also searched the offices of 20 affiliated companies and the home of Yoo Byung-un, the man whose family is believed to be behind the company, looking for any evidence of wrongdoing that could have led to the ship's sinking.
Among other things, investigators have said they will look into whether modifications to the ship in 2013 could have altered the ship's balance and contributed to what happened.
Kim Yong-rok, an opposition lawmaker who represents Jindo, an island near where the ship sank, told CNN that modifications to add 117 more passenger cabins to the ship raised the ferry's center of gravity.
Kim said the work on the ferry took place in 2013 after the Sewol was purchased from a Japanese company. The ferry's passenger capacity was expanded from 804 passengers to 921 passengers, he said.
South Korean prosecutors were unable to confirm those details for CNN.
But they are investigating the private organization responsible for inspecting and certifying ships for the South Korean government, which signed off on the work.
Authorities said they don't yet know precisely what caused the ship to list before it eventually capsized and sank into the ocean on a routine journey from Incheon to the island of Jeju.
They say it didn't appear that the ferry 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 raised from the waters of the Yellow Sea.
A solemn return to school
On Thursday, the return to classes at Danwon High School was steeped in grief.
About two-thirds of the passengers on the Sewol were students at the school in Ansan near Seoul.
Many of them, from the school's second grade, are dead or missing. Several teachers were also lost in the disaster.
On Thursday morning, a series of black hearses drove through the school gates. In each one, a person in the passenger seat held a portrait of a dead student. A bus with tinted windows followed behind carrying relatives and friends.
They were making one last symbolic trip to the school. After the visit, the somber convoys drove on to the students' funerals.
'I want to see you'
At the school's entrance stood a makeshift shrine of flowers and food treats. Hundreds of notes held messages to the dead and missing students.
"Big brother, you have to live, you have to come back." implored one.
"I want to see you," another said. "I love you and pray for you."
Many of the messages from other students expressed regret at not being able to help their classmates in their hour of need.
Thousands of yellow ribbons were tied to the school gates, as well as nearby trees and posts. The ribbons have become symbols of hope that survivors might still be found in the submerged vessel, picking up a practice used in the United States for soldiers and hostages overseas.
The third-grade students, who are in the final year of high school in South Korea, aren't going back to regular classes. The local health service has provided therapists to speak with the teenagers about grief and loss.
First-grade students are expected to return next week. It's unclear when the handful of students in the second grade who didn't go on the ill-fated field trip, and those who survived the sinking, will resume classes.
The students who arrived at the school Thursday had to pass a throng of journalists. Many of them had hoods or caps covering their faces.
CNN's Nic Roberston reported from Jindo, South Korea, and CNN's Michael Pearson reported and wrote from Atlanta. CNN's Will Ripley, K.J. Kwon, Andrew Stevens, Steven Jiang, Kyung Lah, Tim Schwarz, Stella Kim and Judy Kwon also contributed to this report.