By the time federal investigators searched the Manhattan home of Rudy Giuliani on Wednesday, they had amassed a trove of evidence from his associates in Ukraine, focusing most intently on Giuliani’s ties to Ukrainian oligarchs, three witnesses in the case told TIME. The witnesses, who spoke on condition of anonymity, described lengthy interviews with investigators in Europe, Manhattan and Washington, starting in the fall of 2019 and continuing through February. What interested investigators most of all was the relationship between Giuliani and the Ukrainian businessman Dmitry Firtash, who is wanted in the U.S. on corruption charges, this witness says. “The main things that interested them was: How would you assess, how would you describe, what do you know about his communication with Ukrainian oligarchs,” says this witness, who spoke repeatedly to investigators over the course of more than a year. “Firtash was of course their main focus, without a doubt.” Firtash’s goal was to avoid extradition to Chicago, where he faces charges related to an alleged scheme to bribe officials in India.