Ukrainian anti-corruption investigators will seek to question departing Donald Trump campaign chairman Paul Manafort as part of a widening investigation into $12.7 million in payments allegedly designated for him from a secret account kept by the political party headed by the country’s former pro-Russian president, Viktor Yanukovych, the head of a panel overseeing the probe told Yahoo News.

Officials of the National Anti-Corruption Bureau of Ukraine “have to interrogate him. … This has to happen,” said Serhiy Leshchenko, chief of the Ukrainian Parliament’s anti-corruption subcommittee, in an interview from Kiev on Friday, hours after Manafort announced his resignation as chairman of the Trump campaign.

Leshchenko held a Friday press conference in Kiev, where he presented new details about the $12.7 million in payments that were found in an 800-page “black book” from Yanukovych’s “Party of Regions.” Leshchenko told Yahoo News that ledgers in the book include 22 separate entries for Manafort — most of them for fees under his contract as a political consultant to the party, but others for exit polls, computers, international observers and other expenses. On seven of those entries, there were signatures indicating that the money was received for Manafort by Vitaly Kalyuzhny, a former member of Parliament who also served on the board of the European Centre for a Modern Ukraine, a Brussels-based nonprofit. As reported by Yahoo News this week, Manafort hired Washington lobbyists to represent the nonprofit between 2012 and 2014 to improve Yanukovych’s image.

Manafort has denied he received any “off the books cash” payments from the Party of Regions, saying all his payments were for his “entire political team,” including expenses for polling, research and television advertising.

Earlier in the day, Trump announced Manafort’s departure in a statement.

“This morning Paul Manafort offered, and I accepted, his resignation from the campaign. I am very appreciative for his great work in helping to get us where we are today, and in particular his work guiding us through the delegate and convention process. Paul is a true professional and I wish him the greatest success.”

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Manafort had officially taken over the GOP nominee’s operation after Trump fired campaign manager Corey Lewandowski in June. But earlier this week, Trump suddenly elevated pollster Kellyanne Conway to campaign manager and Breitbart News executive Stephen Bannon to campaign CEO — an apparent demotion for Manafort.

That shakeup occurred after Trump struggled to regain his footing following last month’s political conventions. A series of firestorms, including Trump’s public feud with a Gold Star family and his provocative quip about “Second Amendment people,” have since roiled his White House bid. The most recent RealClearPolitics average of national polls gives Democrat Hillary Clinton a 6-point lead over Trump.

The news of Manafort’s resignation was immediately hailed by Alexandra Chalupa, the former Democratic National Committee consultant whose personal emails were hacked after she began conducting “opposition research” on Manafort’s Ukrainian connections last spring.

“I’m ecstatic that Paul Manafort resigned from the Trump campaign,” Chalupa told Yahoo News. “Mr. Manafort is someone who spent the last decades working against our nation’s foreign policy interests overseas, as most recently demonstrated in Ukraine when he worked for Putin’s former puppet president, Viktor Yanukovych.”

Former Trump campaign chair Paul Manafort at the Republican Convention in Cleveland. (Photo: Carlo Allegri/Reuters)

Manafort has also been battling weeks of critical scrutiny, from Yahoo News and other outlets, related to his ties to Russian political interests in Ukraine.

Just days ago, former Congressman Vin Weber, R-Minn., told Yahoo News that Manafort recruited him in 2012 to lobby for the European Centre for a Modern Ukraine.

Weber said that he’d repeatedly asked Manafort for the names of the businesspeople backing the nonprofit, but that Manafort had declined to do so.

It turns out that the backers had close ties to the pro-Russian government of Yanukovych.

“It would be very hard to look at this entity and say it was not directed by the then Ukrainian government,” Adrian Karatnycky, a Ukraine expert at the Atlantic Council, told Yahoo. “It’s pretty clear they were running interference on sensitive issues on behalf of Yanukovych.”