Dossier author Christopher Steele will not cooperate with U.S. Attorney John Durham’s investigation into the origins of the Trump-Russia probe, telling an audience at Oxford University that he believes U.S. investigators have acted in “bad faith.”

Steele, a former British spy, said at the Oxford event on Friday that he and his firm, Orbis Business Intelligence, had already “done our duty” by cooperating with a Justice Department inspector general’s (IG) investigation of the FBI’s surveillance of Trump campaign aide Carter Page.

According to The Daily Beast, which attended the Oxford event, Steele also criticized the IG, saying that he cooperated with the probe for “four or five months,” and observed “very bad qualities” on the part of government officials. He said some acted in “bad faith.”

Reuters reported on Friday that Durham’s team has recently approached Steele seeking an interview. The former MI6 officer rejected the request because he believes that he would not be treated fairly, three sources familiar with the matter told Reuters.

Numerous questions remain unanswered about how Steele collected information for his dossier, and how many of his allegations about Trump associates turned out to be inaccurate.

Steele alleged that the Trump campaign, including Page, took part in a “well-developed conspiracy of cooperation” with the Kremlin to influence the 2016 election.