President Donald Trump’s personal attorney and confidant, Michael Cohen, is scheduled to speak next week with investigators from the Senate Intelligence Committee in a closed-door meeting.

Cohen has been subpoenaed by lawmakers investigating Russia’s attempts to influence the 2016 presidential election and possible collusion with the Trump campaign. He is expected to speak with investigators on Sept. 19. That hearing will not be open to the public.

Cohen, 51, emerged as an important figure in the investigation after he was named in a 35-page dossier alleging Russia and the campaign worked together to help get Trump elected. That document was researched and written by a former British spy and published by BuzzFeed News in January after top law enforcement officials had briefed President Barack Obama and Trump, who was then president-elect, about it. The dossier asserted that Cohen visited Prague to meet with Kremlin officials and was an important player in the “ongoing secret liaison relationship” between Russia and the campaign.

Cohen called these claims “profoundly wrong” in a letter sent last month to lawmakers. His passport, which he showed to BuzzFeed News, had no stamps from the Czech Republic. He later told lawmakers that was his only passport.

Cohen urged congressional investigators to “discern and publicly disclose” those who paid for the dossier, and that he has no documents tying him to any of the allegations.

Reached late Tuesday by BuzzFeed News, Cohen declined to comment.

The Trump Organization has turned over documents to congressional investigators, including an email in which Cohen asked a spokesperson for President Vladimir Putin for help advancing a Trump business project. In another email, a business associate boasted to Cohen that he would help get Trump elected and that he could get “all of Putin’s team to buy in on this.”

Cohen has agreed to testify before the House Intelligence Committee as well, and has offered up several dates. So far, no date has been set, and the committee continues to suffer partisan infighting.