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Two Filipino seamen who died two weeks apart during a Japanese coal carrier's voyage to Australia in 2012 were killed by one or more assailants, an Australian coroner said Wednesday.

New South Wales state Deputy Coroner Sharon Freund recommended that her report on the two deaths be sent to Japanese authorities who investigated a third death discovered when the same Panama-flagged carrier, the MV Sage Sagittarius, returned to Japan.

The series of the deaths over five weeks has led to the Sage Sagittarius being dubbed the "Death Ship" by the media. The extraordinary events highlighted difficulties in criminal investigations involving so-called flag of convenience ships, which are registered in countries foreign to their owners, operators and crews. No one has been charged over any of the deaths.

The Filipinos — head chef Cesar Llanto, 42, and chief engineer Hector Collado, 55 — were part of a 25-member all-Filipino crew that left the Japanese port of Kudamatsu aboard the carrier operated by one of the world's biggest shipping companies, Nippon Yusen Kabushiki Kaisha, on Aug. 20, 2012, bound for the Australian port of Newcastle.

Llanto vanished in international waters 10 days later. Freund found that he was either thrown overboard or killed on the ship and his body disposed of later by one or more unknown assailants. His body was never found.

Two weeks after the chef's death, Collado died after falling 11.5 meters (38 feet) from one deck to another as the ship entered Newcastle Harbor. The coroner found Collado, who was second in charge of the ship and potentially a key witness in Llanto's disappearance, had been struck over the head with a weapon by one or more culprits.

The third fatality was Kosaku Monji, a 37-year-old supervisor employed by the ship's Japanese operator who joined the Sage Sagittarius with two security guards four days after the chef disappeared.

Monji was found dead on Oct. 6, three days after the ship returned to Kudamatsu. His body was trapped between a conveyor belt and roller that was unloading coal.

The Japanese coast guard concluded his death was accidental.

The coroner said the evidence "suggests strongly" that the ship's captain, Venancio Salas, caused or authorized Llanto's disappearance or had more knowledge about the circumstances than he revealed during his testimony at the coroner's 11-day hearing.

She said Salas ran his ship "through bullying and intimidation," illegally sold handguns to crew and had been in conflict with Llanto, who was on his first voyage as chief chef and knew of a crew plot to report Salas for misconduct.

"The evidence is overwhelming that there was a climate of fear on board the vessel after the disappearance of Mr. Llanto," Freund wrote. "It would be an extraordinary coincidence if the person(s) who caused Mr. Llanto's death were not also responsible for Mr. Collado's death."

Freund did not investigate Monji because he died outside Australia's jurisdiction. Australian coroners hold court-like hearings into unusual deaths and only the Filipino deaths were investigated by Australian police. Coroners cannot be sued for defamation for their findings.

The International Transport Workers' Federation, a seafarers' union, pointed to the coroner's finding that there were "very significant practical impediments created by a disappearance or death on board a foreign-flagged vessel" in forensic investigations.

"Flag of convenience ships are registered in countries prepared to prostitute their flags, like Panama and Mongolia — in return for tax avoidance, minimum regulation and little or no responsibility, like what we have seen exposed here today," the union's Australian coordinator, Dean Summers, said in a statement.

The ship's Japanese operator said in a statement: "We need time to examine the coroner's findings in detail before commenting further. What we can say is the welfare of our ships' crews is always of the utmost concern to us and we will continue to take all steps to provide a safe working environment."

The Australian government said it would review the coroner's findings.

Salas could not be immediately contacted for comment.