Seattle, Washington - A Texas-based railway company must pay some $400 million to an Indigenous community after it transported crude oil through the group's reservation without authorization, a US judge in Seattle ordered on Monday.

Railway company BNSF – owned by billionaire Warren Buffett – has had permission from the Indigenous Swinomish Indian Tribal Community to use tracks that run through the community's territory in Washington state since 1991, the Seattle Times reported.

However, the agreement stipulates that a maximum of 25 wagons are allowed to pass through per day, and the community must be informed of the type of cargo.

The Swinomish people sued in 2015 after BNSF sent significantly more train cars carrying crude oil to nearby refineries without having received specific permission for the freight or the quantity.

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A previous ruling had already deemed the company to have acted in violation of the 1991 agreement.

In the current case, the court was to determine how much the company earned from the transportation of crude oil as well as the proportion owed to the Indigenous community.

The judge said that it is unclear how BNSF invested its "ill-gotten" profits and what returns were generated as a result. He said he assumes that those responsible made far more profit from their misconduct.

"The court finds that, in the interest of justice and equity, supplemental enhancement in an amount that approximates the money market return is appropriate here," the judge added.

The Swinomish people's territory is situated on the Pacific coast in the north-west of what is now known as the US. Fishing holds significant cultural and economic value for the community.

Last year, a large amount of diesel fuel spilled on their land after two BNSF trains derailed.