The investigators had previously come across the two men, Lev Parnas and Igor Fruman, as they pursued a long-standing case against a Ukrainian gas tycoon accused of bribery, according to two people familiar with the matter. They, like others interviewed regarding the case, spoke on the condition of anonymity to discuss the ongoing litigation.
The Chicago prosecutors reached out to their counterparts in New York, where the foreign money charges had been brought, to offer assistance, the people said.