*Cause of death of S Korea's sunken ferry owner failed to be determined as body was badly decomposed.

*No drugs and toxics were found on Yoo's body, which was also tested negative for alcohol inclusion.

*No signs were detected for being beaten or stabbed to death.

The cause of death of South Korea's sunken ferry owner failed to be determined as the body was badly decomposed, the state forensic agency said Friday.

"It was impossible to identify the death cause of Yoo Byung-eon as his body was badly decomposed," Seo Joong-seok, director of the National Forensic Service, said at a nationally televised press briefing.

The body, which was found on June 12 in the country's southern city of Suncheon, matched that of Yoo, but the death cause was not identified, the director said.

Police said Tuesday that a body was discovered 40 days ago in a plum field in Suncheon, around 415 km south of Seoul, noting it has been confirmed as that of Yoo through DNA testing and fingerprinting.

The police agency in Suncheon first believed it was the body of a homeless person due to its shabby appearance. The belated confirmation has triggered numerous rumors spreading on the Internet such as the body being switched.

The forensic agency said little tissues and muscles would remain when 10 days pass by after the death, stressing there was no switch of the body between the first and second autopsy.

According to the toxicology test and autopsy conducted by the agency, no drugs and toxics were found on Yoo's body, which was also tested negative for alcohol inclusion.

No signs were detected for being beaten or stabbed to death. Whether he had been strangled to death cannot be determined, the agency said.

Yoo, 73, owned Chonghaejin Marine, the operator of ferry Seowl which capsized and sank off the southwestern coast on April 16. The deadliest maritime disaster left more than 300 people, mostly high school students, dead or missing.

Yoo and his family have been suspected of committing a host of illegal acts such as embezzlement, dereliction of duty and tax evasion, which led to lack of funds in the ferry operator and caused lax safety practices such as the inveterate overloading.

A massive manhunt was launched after the ferry disaster as Yoo and his family dismissed prosecutors' summons several times and ran away.

Arrest warrants were issued for Yoo's second son and eldest daughter, who are staying abroad, and Yoo and his eldest son have been placed on the most wanted list.