The New Yorker has a long article about Lutsenko, which includes information and quotes about Giuliani:
https://www.newyorker.com/magazine/2019/12/23/the-ukrainian-prosecutor-behind-trumps-impeachment
Excerpt:
"In a long conversation with me this past November, Giuliani largely confirmed Lutsenko’s account of their relationship. He, too, saw Yovanovitch as an obstacle, hindering his attempt to dig up dirt against his client’s rival in advance of the 2020 election. “I believed that I needed Yovanovitch out of the way,” he said. “She was going to make the investigations difficult for everybody.” Giuliani compiled a dossier on the Bidens and Yovanovitch, which he sent to Secretary of State Mike Pompeo, and which was shared with the F.B.I. and with me. John Solomon, a journalist, had interviewed Lutsenko for the Washington-based publication The Hill. Giuliani promoted the project. “I said, ‘John, let’s make this as prominent as possible,’ ” Giuliani told me. “ ‘I’ll go on TV. You go on TV. You do columns.’ ”
Initially, Lutsenko and Giuliani seemed a perfect partnership; the meeting between them, Lutsenko told me, offered a “win-win” situation. But by May each man felt that he had been led on by the other. After Giuliani failed to arrange a meeting with Attorney General William Barr, who had succeeded Sessions, and Lutsenko failed to publicly announce a Ukrainian investigation into the Bidens, Trump made his fateful July 25th call to the new Ukrainian leader, Volodymyr Zelensky, to request that he announce a probe into the Bidens and the 2016 election. In September, the disclosure of Trump’s request by a whistle-blower led Nancy Pelosi, the House Speaker, to launch the impeachment inquiry. Three weeks later, F.B.I. agents arrested Parnas and Fruman, who face charges of conspiracy, making false statements, and falsification of records. The F.B.I. has now reportedly turned its attention to Giuliani.