MOKPO, South Korea — The captain and three senior crew members of a South Korean ferry that capsized in April, killing more than 280 passengers, many of them school children, were indicted for homicide on Thursday, a senior prosecutor said.

Prosecutors also indicted the 11 other surviving crew members of the ferry Sewol on negligence charges. The crew has been under criminal investigation after they were believed to have escaped the sinking vessel before many passengers.

"The captain, a first officer and second officer and the chief engineer escaped before the passengers, leading to grave casualties," prosecutor Ahn Sang-don, who is leading the investigation, told a news briefing.

Ahn said the Sewol was severely compromised in its ability to maintain stability after a remodeling to add capacity, and had set sail on April 16 massively overloaded and with insufficient water in the ballast tanks used to keep it steady.

Strong currents in the disaster zone made the vessel less responsive to navigation and prompted the crew to make a turn of 15 degrees, sharper than advisable, which led the ferry to list rapidly and then sink, he said.

"The captain should have been in command of the navigation, but left that to a third officer, and that is gross negligence," Ahn said, adding there was enough evidence to support a charge of willful negligence on the part of the captain and three other officers.

"The charge of homicide was applied because they did not exercise their duty of aid and relief, leading to the deaths of passengers," he said, adding that some crew had confessed "they were thinking about their own lives."

The Sewol was on a routine journey from the mainland port of Incheon to the southern holiday island of Jeju.

Of the 476 passengers and crew on board, 339 were children and their teachers on a school trip. Only 172 people were rescued, with the rest presumed to have drowned.

A month after the disaster, 281 bodies have been recovered but 23 people remain missing, even as rescue divers continue to search the vessel.

Some of the crew, including the captain, were caught on videotape abandoning ship while the children were repeatedly told to stay put in their cabins and await further orders.

The government of President Park Geun-hye has faced sharp criticism for its handling of the disaster and the rescue effort, with an outpouring of anger over suggestions that a more effective initial response could have saved many more.

Prosecutors are seeking the arrest of members of the family that owns the ferry operator, and may also seek the extradition of a son of the reclusive head of the family from the United States, an official said on Thursday.

Prosecutors are also investigating officials of shipping inspection agencies and the operator of the ferry. The crew members' first court date has yet to be set.