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HELSINKI (AP) — The Estonian and Swedish accident investigation boards said Tuesday that a research expedition earlier this year to the wreck of a ferry that sank in the Baltic Sea 27 years ago hasn’t provided new evidence contradicting the official accident investigation report.

In one of Europe’s deadliest peacetime maritime disasters, the M/S Estonia sank in heavy seas on Sept. 28, 1994, killing 852 people, most of them Swedes and Estonians. The ferry was en route from Estonia’s capital, Tallinn, to Stockholm when it sank about 30 minutes after an initial distress call.

Only 137 people on board survived. The fate of the vessel has sparked several conspiracy theories, including that it might have collided with a submarine or that it allegedly carried sensitive military cargo.

The 1997 official joint investigation by Estonia, Finland and Sweden concluded that the ferry sank when its bow door locks failed in a storm. That separated the bow door from the vessel, opening up the ramp to the car deck and causing extensive flooding of the decks.

However others had questioned this amid increasing evidence that there was a large hole in the ferry.

Presenting the preliminary results of a dive by underwater robots in July, Rene Arikas, head of the Estonian Safety Investigation Bureau, said that the dive revealed that the wreck does have a hole, about 22 meters (72 feet) long and 4 meters (13 feet) high. The wreck is resting on a slope on the seabed and its original position has changed over the years due to changes in the seabed, making the hole and other damage more visible, he said.

Despite this, he stressed during a news conference in Tallinn that researchers have no evidence proving the official report on the sinking to be incorrect.

New underwater surveys are scheduled in March or April when visibility is considered the best, Arikas said.

Jonas Backstrand, deputy director general of Sweden’s Accident Investigation Board, said researchers were surprised to find the seabed to be substantially rocky, and this could well be the reason for the hole.

“We don’t know how this damage (to the vessel) occurred,” Backstrand said, but it was likely when the vessel fell onto the rocky seabed. More investigation is needed, he said.

A separate, privately funded expedition commissioned by relatives of the victims of the M/S Estonia conducted a dive in September. Initial results of that dive are expected to be published early next year.

The wreck lies on the seabed 80 meters (265 feet) below the surface in international waters off a Finnish island, and is considered a graveyard, which gives the area protection under the law.