Special Counsel Robert Mueller is investigating whether former Trump campaign chairman Paul Manafort had “back channels” to Russians trying to interfere with the 2016 U.S. election, a lawyer for the Department of Justice told a judge on Thursday.

“He had long-standing ties to Russia-backed politicians,” Michael Dreeben, a lawyer for the department, told U.S. District Judge Amy Jackson on Thursday, Bloomberg reported. “Did they provide back channels to Russia? Investigators will naturally look at those things.”

Until now, prosecutors in the case against Manafort haven’t explicitly spelled out that possible connection between Manafort and Russia’s political elite. Mueller’s team has, however, made note of Manafort’s business ties to Russian oligarch Oleg Deripaska.

The comment was made during a hearing over whether Mueller exceeded his authority by charging Manafort with financial crimes related to Manafort’s previous work as a political consultant for the former President of Ukraine, Viktor Yanukovych.

Manafort, 69, has tried to have the charges against him dismissed by arguing that they aren’t related to Mueller’s central mandate — investigating Russian meddling and possible collusion by the Trump campaign.

Congressional investigators have been probing the relationship between Manafort, Deripaska and Manafort’s longtime right-hand man in Ukraine, Konstantin Kilimnik, people familiar with the matter told VICE News in late March.

Dreeben’s remarks came during testimony before Judge Jackson in Washington DC on Thursday, Peter Carr, spokesman for the Special Counsel, told VICE News. Carr said he could not immediately confirm Dreeben’s exact comments in the courtroom on Thursday. But he said the argument aimed to summarize the government’s response to Manafort’s attempt to dismiss the case.

In an email to VICE News, Carr highlighted language from a filing made by Mueller’s team in early April.

“An investigation of possible ‘links and/or coordination’ between the Russian government in its political-interference campaign and ‘individuals associated with the campaign of President Donald Trump’ would naturally cover ties that a former Trump campaign manager had to Russian associated political operatives, Russian-backed politicians, and Russian oligarchs.”

“It would also naturally look into any interactions they may have had before and during the campaign to plumb motives and opportunities to coordinate and to expose possible channels for surreptitious communications,” the document continues. “And prosecutors would naturally follow the money trail from Manafort’s Ukrainian consulting activities. Because investigation of those matters was authorized, so was prosecution.”

In February, Mueller indicted Manafort on 32 counts of tax and financial fraud in a court in Virginia, following an original indictment filed in Washington, DC. Manafort has pleaded not guilty to all charges.

Manafort spent years working for Yanukovych, helping revamp his political image in Ukraine after a devastating loss in presidential elections in 2004. With Manafort’s help, Yanukovych captured the presidency in 2010.

Yanukovych has been widely seen as close to Moscow, and he fled to Russia after protests in Ukraine topped his government in 2014.

Roughly a decade ago, Manafort also provided Russian oligarch Deripaska with investment and consulting services before their relationship soured. In January, a company controlled and funded by Deripaska sued Manafort and and his longtime business partner Rick Gates for at least $25 million in damages connected to a failed joint cable and internet venture in Ukraine, according to court documents.

Deripaska has flatly denied being in communication with Manafort around the 2016 election.