A Colombian judge sentenced Jaime Blanco, who ran a food services concession at a Drummond mine, to nearly 38 years in prison after finding him guilty of being the mastermind behind the 2001 murders.

According to the Associated Press, Drummond union president Valmore Locarno, 42, and vice president Victor Hugo Orcasita, 36, were shot to death by far-right paramilitaries on a company bus home after a shift at one of Drummond's La Loma mines in the northern state of Cesar.

The case has drawn considerable attention because Blanco and several others involved allege that senior managers of the Alabama-based company ordered the murders.

A related lawsuit in the US is underway to determine the company’s involvement and Blanco is a key witness in that case.

The class action lawsuit, filed by more than 600 alleged victims and relatives, claims that Drummond aided and abetted war crimes, including extra-judicial killings.

In March last year a former Colombian paramilitary testified that the coal giant gave $US1.5 million to his arm of the paramilitary to murder union leaders.

Drummond denies hiring militia as well as any involvement in the 2001 murders but is yet to provide further comment.

The news coincides with suspension of the miner’s loading license at the port of Santa Marta following a government claim the miner covered up a coal spill off the country’s northern coast last month.

Colombia’s environmental licensing agency reportedly imposed the “preventative measure” against Drummond after it dumped 870 tonnes of cargo.

Licensing agency directory Luz Helena Sarmiento told Bloomberg the suspension would last “until they update their contingency plan”

Under Colombian environmental license regulations, all such incidents are required to be reported within three days.

An inquiry began 17 days after the spill, with allegations of a cover-up due to Drummond’s lack of formal disclosure to the government.

While Drummond did not release a public statement responding to the report, the company told local media the crew dumped the coal in an effort to save human life and keep the barge from sinking.

“International marine protocols emphasize saving human lives first,”Bloomberg quoted from a company statement.

“Workers proceeded to extract from the barge water that had mixed with coal.”

Drummond mines most of its coal in Colombia where it controls a 2 billion ton resource.

Its deepwater terminal at Santa Marta handles thermal coal from the company’s five Colombian operations at Mina Pribbenow and the El Descanso open pit, which together produce 25 million tons of coal a year for export to the US and Europe.