The Department of Justice recently asked a prestigious U.S. law firm for documents and information related to its work for deposed Ukrainian President Viktor Yanukovych, on whose behalf Paul Manafort, President Donald Trump’s former campaign chairman, also worked, the New York Times reported on Thursday.

The New York Times reported, citing two unnamed sources with direct knowledge of the matter, that the Department of Justice asked Skadden, Arps, Slate, Meagher & Flom for information and documents relevant to its work on Yanukovych’s behalf.

According to the report, former Justice Minister Oleksandr Lavrynovych, an ally of Yanukovych, hired the law firm to produce a report justifying the imprisonment of former Ukrainian Prime Minister Yulia Tymoshenko, Yanukovych’s political rival.

The New York Times reported, citing unnamed consultants involved in the strategy to justify Yanukovych’s actions, that Manafort worked on recruitment for the effort and “devised the strategy” of which the law firm’s report was an element.

“Whoever commissioned this study, whatever the mandate for the study was, it was incomplete and doesn’t give an accurate picture,” a State Department spokesman said in 2012 of the final report the law firm produced, published the same year.

As the New York Times noted in its report, it was not clear whether the Department of Justice’s request was related to special counsel Robert Mueller’s investigation into Russian interference in the 2016 election, which has focused in recent months on Manafort.

According to the New York Times, Ukrainian prosecutors asked the Department of Justice for help with an investigation into alleged illegal spending by Yanukovych’s government. The current Ukrainian government claims that Yanukovych stole at least $1 billion before leaving office. Manafort in July filed financial reports reflecting that he earned nearly $17 million for his work on behalf of Yanukovych’s pro-Russia Party of Regions.

Ukrainian prosecutor general Yuriy Lutsenko’s office told the New York Times recently, according to the report, that his office was working with the Department of Justice to investigate payments the department’s Ukrainian counterpart made to the law firm, but was less forthcoming when asked whether Ukrainian prosecutors were working with Mueller on his investigation.

Lutsenko’s office told the New York Times that it had not publicly disclosed any cooperation of the sort, but also noted that not all such cooperation may be disclosed.

Reached for comment by TPM, a spokesperson for the special counsel declined to comment. Neither the Department of Justice nor a spokesman for Manafort immediately responded to TPM’s requests for comment.

Mueller has reportedly sought other documents related to work overlapping with Manafort’s in the region. In August, the Washington Post reported that lawyers for the special counsel issued subpoenas to Washington lobbying firms that interacted with firms led by Manafort and Trump’s former national security adviser Michael Flynn, who was ousted over misstatements about his own conversations with a Russian official.

The New York Times reported, quoting an unnamed source familiar with those inquiries, that the subpoenas focused on “Manafort’s money — where it came from, how he got it, what he did with it.”

Manafort himself appears to be a particular target of Mueller’s probe, or at least a subject of specific interest in the investigation.

The New York Times on Monday reported that shortly after FBI agents raided Manafort’s home in July, Mueller’s team warned Trump’s former campaign chair to expect an indictment. Federal investigators’ interest in Mueller’s Ukrainian work predates the probe into Russia’s election interference. CNN on Monday reported that the federal government wiretapped Manafort for a period starting in 2014 as part of an investigation into Yanukovych. The surveillance ended in 2016, only to be restarted again that year and continued through the beginning of 2017.

The Washington Post on Wednesday reported that Manafort offered private briefings on the Trump campaign to a Kremlin-tied Russian billionaire, with whom Manafort had a previous business relationship.

And the New York Times on Wednesday reported that Manafort was working for Kurdish Iraqis advocating for an independence referendum that runs counter to the U.S. government’s stated interests in the region, work he apparently began around the time of the FBI raid on his home.