Forensic scientists and detectives are trying to unravel the mystery of a “ghost ship” filled with skeletons that washed up on the coast of Japan this weekend.

The boat was found late on Sunday on the shores of Oga, Akita Prefecture, on Japan's west coast (video below). Japanese broadcaster NHK reports that the 7-meter-long (23-foot-long) boat contains the decomposing bodies of eight people. The vessel also has an eight-digit number painted on the side, a broken rotor blade, and no signs of fishing equipment.

One of the big challenges facing authorities is the identification of the bodies. The bodies are partially skeletonized, so much so it’s not possible to discern the age or sex of the crew. The partial skeletonization of the bodies suggests the bodies are in the third of five stages of decomposition, called active decay. This is the stage where much of the body’s tissues are lost through liquefaction by microorganisms and maggots, resulting in bones becoming exposed. This usually indicates the body has been dead for a few weeks. Depending on the conditions, it takes several months or years for a human body to completely skeletonize. However, considering this boat has been out in the cold and remote sea, the normal “rules” don’t necessarily apply.

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Although much of the story still remains a mystery, they highly suspect that the ship is from North Korea. Firstly, the Japanese coastguards do not know of any missing Japanese vessels. Ota, where the boat washed ashore, is also directly eastward of the coast of North Korea. Onboard the ship, they also found a packet of cigarettes that are believed to have been produced in North Korea.

This boat washing ashore comes just days after another North Korean ship washed ashore. Last Friday, eight live North Korean sailors washed ashore in the northeastern Japan prefecture of Akita. Over the weekend, two more bodies were found washed ashore on a beach just 70 kilometers (44 miles) southwards. Once again, they are suspected of being from North Korea. In 2014, at least 65 “ghost ships” washed up in Japan, and the year before there were 80 reports, according to the Japan Times

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Some believe these “ghost ships” are the result of North Koreans fleeing the notoriously repressive rule of Kim Jong-Un. Equally, commentators have noted that the regime is pushing fishermen to produce greater amounts of food and forcing them to venture into more treacherous seas to help deal with the country’s chronic food shortages.

“During the summer, the Sea of Japan is quite calm," Yoshihiko Yamada, professor at Japan’s Tokai University, told Reuters. "But it starts to get choppy when November comes. It gets dangerous when northwesterly winds start to blow."