SEOUL, South Korea — The eldest son of the South Korean business mogul who controlled the company that ran the Sewol ferry, which sank in April, leaving more than 300 people dead, was convicted of embezzlement on Wednesday and sentenced to three years in prison.

The son, Yoo Dae-kyoon, 43, was convicted of taking nearly $6.8 million since 2002 from seven companies controlled by his family, including Chonghaejin Marine Company, which operated the Sewol ferry. Mr. Yoo’s father, Yoo Byung-eun, was a fugitive facing similar embezzlement charges when he was found dead in July.

The sinking of the Sewol on April 16, in waters off southwest South Korea, was the country’s worst disaster in decades. Most of those killed were high school students on a field trip. The authorities accused members of the Yoo family of stealing the equivalent of millions of dollars from the Chonghaejin ferry company alone, money they said could have been used for safety measures that were not put in place on the Sewol.

Prosecutors also said that the ferry operator had overloaded its ships, including the Sewol, in part to help make up for the losses incurred by the family’s embezzlement. Investigators said the Sewol was carrying twice as much cargo as it was allowed.

Yoo Dae-kyoon “abused his status as a son” of his charismatic father to embezzle the money, a court in Incheon, a port city west of Seoul, said in its ruling on Wednesday.

Prosecutors said members of the Yoo family, along with their deceased patriarch, embezzled $169 million from a church that Yoo Byung-eun helped found and from a fleet of companies, including Chonghaejin, that were run with the use of church funds and with loyal church members installed as business executives.

Two of Yoo Byung-eun’s brothers were also convicted of embezzlement on Wednesday. One, Yoo Byung-il, who was convicted of taking $119,000 from Chonghaejin, received a suspended sentence. The other, Yoo Byung-ho, was sentenced to two years in prison for taking $2.7 million from another family-controlled company. Thirteen executives from companies controlled by the family were convicted of aiding in the embezzlement, with four sentenced to prison terms of two to four years and the others receiving suspended sentences.

A daughter of Yoo Byung-eun, Yoo Some-na, was arrested in Paris in May and is fighting extradition to South Korea. The South Korean authorities have asked the United States Justice Department for help in apprehending another son, Keith H. Yoo, who they say lives in America.

Four senior members of the Sewol’s crew, including the captain, are on trial on murder charges in the city of Gwangju. Prosecutors said the senior crew members did little to help the passengers escape the sinking ferry, though they had the means to do so. Investigators and survivors of the disaster said passengers were repeatedly told to stay inside the ship as it sank. Eleven other crew members face lesser charges. Verdicts in that trial are scheduled for Tuesday.