Former mining contractor Jaime Blanco has been convicticted of murder over the 2001 killing of two trade union leaders and sentenced to 38 years in prison.
The Colombian court also ordered prosecutors to investigate US mining company Drummond's president and three former employees to determine whether they might also be responsible.
The January 25 verdict only emerged today and is now under appeal.
The killings are the subject of a US lawsuit and have drawn considerable attention because several witnesses, including Mr Blanco, have alleged that senior managers of Alabama-based Drummond ordered them.
Drummond officials have denied any involvement in the killings.
Union leaders Valmore Locarno and Victor Hugo Orcasita were shot dead after being pulled from a workers' bus by far-right paramilitaries after a shift at Drummond's La Loma mine in the northern Colombian state of Cesar.
Human rights and trade union activists allege that Drummond colluded with paramilitary militias blamed for thousands of murders in Colombia, hiring them to silence opponents and suspected leftist rebels.
The company denies hiring militias and is fighting a lawsuit filed by survivors of the murdered men in an Alabama federal court that claims Drummond aided and abetted war crimes, including extra-judicial killings.
Judge William Castelblanco sentenced Mr Blanco, who ran a food services franchise at the Drummond mine, to 37 years and 11 months in prison and fined him $369,000 (£234,000).
The judge said in an 81-page opinion that Mr Blanco "took advantage of his closeness to commanders of the paramilitaries" to help him eliminate Mr Locarno and Mr Orcasita, who represented trade union members who had complained about the food service.
Mr Blanco told reporters in April 2011 that Drummond's senior management had ordered that the two union organisers be killed.
Lawyer for the plaintiffs Terry Collingsworth applauded judge Castelblanco's order that prosecutors investigate Drummond's president, Garry Drummond, as well as a former mine security chief and two Colombians to determine whether they shared responsibility for the killings.
But he also said he wasn't hopeful that the order would lead to a Colombian criminal prosecution.
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