Investigators on Friday said that a junior officer was at the helm of South Korean ferry Sewol when it capsized on Wednesday, and that the captain of the vessel, Lee Joon-seok, may have been away from the bridge at the time of the tragic accident.        

The ferry was transporting 475 passengers and crew on a trip from the Korean mainland to Jeju, a vacation island. The official death toll has climbed to 25, yet 271 people, including many schoolchildren, were still unaccounted for Friday, Reuters reported.

Investigators have focused on the role of the Sewol's 69-year old captain and the crew of the ferry, which apparently had a clean safety record when it capsized in shallow, calm waters, the news agency said. Lee, who faces a criminal investigation, hasn't made a public statement on whether or about why he may have left the boat before many passengers exited the vessel. 

"He [the captain] may have been off the bridge.. And the person at the helm at the time was the third officer," Park Jae-eok, an official investigating the accident, told a press conference in Mokpo, a city close to the port where rescue operations are being conducted.

"It is not clear where [the captain' 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, according to CNN.

Rescuers began pumping oxygen into the Sewol on Friday and three cranes were in transit to the site of the deadly accident, where they would set up later in the day in order to salvage the sunken ferry, Reuters reported.

The parents of missing schoolchildren aimed blame at the captain for the tragic accident after he and officials of a shipping company offered emotional apologies for the loss of life.

According to witnesses, the captain and some crew members exited the ferry while others crew members instructed passengers to stay in place as the boat sank in just over two hours while it was located about 25 kilometers (16 miles) southwest of Jindo, a large island connected to South Korea's mainland.              

Theories about the cause of the disasters have been swirling, and investigators have declined to comment on reports that the vessel had turned before it listed to port and capsized.

Coastguard officials have said that the investigation was focused on possible crew negligence, structural defects of the ship and cargo stowage problems, even though the ferry appears to have passed all of its safety and insurance checks, Reuters noted.

Most of those on board were children from a high school in the suburbs of Seoul who were on a field trip to Jeju.              

Relatives were in mourning overnight in a hospital in the city of Mokpo, near the city of Jindo, which is serving as a rescue center. Some spoke quite bitterly of Lee.

"How could he tell those young kids to stay there and jump from the sinking ship himself?" said Ham Young-ho, grandfather of 17-year-old Lee Da-woon, one of the dead, Reuters reported.               

Search-and-rescue efforts continued on Friday amid dreary conditions, CNN reported.

No one was rescued on Thursday, when two U.S. Navy helicopters with special radar were only able to fly several hours because of the bad weather, and when divers contended with robust currents, extremely cold water and difficulty seeing, the news site said.

"It's extremely difficult," Agle, who said the Navy helicopters were from the USS Bonhomme Richard nearby, according to CNN. "There are heavy currents in the area, so the vessel itself is not stable in the water. So you are, by default, putting divers at risk... There are many, many things that are working against them."

In Jindo, meanwhile, the parents and guardians of more than 300 high school students who were on the ferry are experiencing a different kind of struggle, according to CNN. Some insisted on getting answers from Lee Joon Suk as they exclaimed, "Captain, come out."

While he didn't talk directly to the parents, he did speak at a South Korean Coast Guard office on Thursday. He broke down in tears in front of reporters, saying only, "I am sorry, I am at a loss for words."