Former CIA director John Brennan was interviewed for eight hours Friday by the federal prosecutor specially assigned by Attorney General William P. Barr to review how the U.S. intelligence community and law enforcement apparatus handled investigating Russian interference in the 2016 election, answering questions on a “wide range” of topics, including the intelligence community’s assessment that Russia intended to help Donald Trump become president, a Brennan adviser said.

In a statement, Nick Shapiro, Brennan’s former deputy chief of staff, said U.S. Attorney John Durham informed Brennan he was “not a subject or a target of a criminal investigation” but rather “a witness to events that are under review.”

Barr tapped Durham more than a year ago to review the FBI’s 2016 probe into possible coordination between Russia and the Trump campaign. Since then, Durham has questioned FBI and intelligence community witnesses on many topics, including why the FBI opened the probe in the first place and why the bureau pressed forward as one aspect, an examination of former Trump campaign adviser Carter Page’s ties with Russia, seemed to produce no real results.

He has also asked about the intelligence community’s January 2017 assessment that the Russian interference operation was ordered by Russian President Vladimir Putin — and designed to help Trump.

In the statement, Shapiro said Brennan, who was interviewed at CIA headquarters, “welcomed the opportunity to answer Mr. Durham’s questions,” some of which were about that assessment.

“Brennan provided details on the efforts made by the Intelligence Community to understand and disrupt the actions taken by Russia to interfere in the 2016 presidential election,” Shapiro said. “Brennan expressed appreciation for the professional manner in which Mr. Durham and his team conducted the interview.”

But Shapiro indicated that Brennan, who served as CIA director from 2013 to 2017, also expressed some skepticism about the Durham review, asking “why the analytic tradecraft and the findings of the [intelligence community assessment] are being scrutinized by the Department of Justice,” particularly in light of the findings by special counsel Robert S. Mueller III and the bipartisan Senate Intelligence Committee about how Russia showed a willingness to aid the Trump campaign, and the Trump campaign a willingness to use that to its advantage.

Brennan, according to Shapiro, “also told Mr. Durham that the repeated efforts of Donald Trump and William Barr to politicize Mr. Durham’s work have been appalling and have tarnished the independence and integrity of the Department of Justice, making it very difficult for Department of Justice professionals to carry out their responsibilities.”

Durham’s investigation has long been politically fraught. Democrats have asserted that it is meant to undermine an investigation merely because it long dogged Trump’s campaign and presidency, while conservatives, including Trump, have publicly clamored for charges against high-ranking FBI and intelligence community officials who worked in President Barack Obama’s administration. Barr notably has said he will not delay the investigation’s findings until after the election, drawing charges from Democrats that he is trying to use law enforcement to influence voters.

Justice Department policies counsel prosecutors not to take steps that can influence an election, though they do not offer any specific prohibitions, particularly in cases where no political candidates are at issue. Barr has said specifically that Obama and former vice president Joe Biden, who is running against Trump, are not being investigated.

“It is Brennan’s fervent hope that the results of the Durham review will be apolitical and not influenced by personal or partisan agendas,” Shapiro said.

This week has been a busy one for Durham. On Wednesday, a former FBI lawyer pleaded guilty to doctoring an email that was used as the bureau sought court permission to secretly monitor Page, marking the first criminal case Durham has brought.

Spokespeople for Durham and Barr declined to comment.