When Newsnight confronted Mr Grossman about his vulture fund operation, he said: "I'm not beating up the Congo. I'm collecting on a legitimate claim."
However, a joint BBC Newsnight/Guardian newspaper investigation has established that the debt in question, which was originally a loan from Yugoslavia to Zaire 30 years ago, was illegally sold to Mr Grossman's fund, FG Hemisphere.
Zufer Dervisevic, who is the chief of the financial police in Bosnia, told journalists: "Of course it was illegal," and said that the man who organised the sale, former Bosnian Prime Minister Nedzad Brankovic, "should go to jail".
Mr Brankovic was prime minister of Bosnia until he was indicted for separate corruption charges - charges of which he was acquitted last year.
The Centre for Investigative Reporting in Sarajevo obtained a police report, which is now with prosecutors, recommending that Mr Brankovic be prosecuted for his part in the sale of the loan to FG Hemisphere.
Bosnian police showed the Newsnight/Guardian team paperwork which reveals that FG Hemisphere paid $3.3m for the claim, of which more than a half a million went to another "vulture" operator who helped set up the deal - Michael Sheehan, an American who calls himself "Goldfinger" after the James Bond villain.
Asked by reporter Greg Palast whether he thought it was fair to take $100m from Congo for a debt for which he had paid $3m, Mr Grossman said: "Yeah, I do actually," but he denied paying just $3m for the claim.
Mr Grossman also said he did not know that the Bosnian police said the loan had been illegally sold to him.
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