Facebook CEO Mark Zuckerberg on Tuesday confirmed that Facebook is working with the special counsel investigating Russian meddling in the 2016 election and potential collusion with the Trump campaign.

The revelation came during Zuckerberg’s appearance in front of the Senate Commerce, Science and Transportation Committee and Senate Judiciary Committee joint hearing on Facebook.

Asked by Sen. Pat Leahy (D-VT) whether the special counsel team had subpoenaed Facebook, he responded, “I actually am not aware of — of a subpoena. I believe that there may be, but I know we’re working with them.”

During the more than five-hour hearing, Democrats sought to cast blame on Facebook for allowing Cambridge Analytica to possibly influence the campaign.

Cambridge Analytica is a political data firm the Trump campaign hired to target audiences with campaign ads. A Russian-American psychology professor at the university built an app that would harvest data for Cambridge Analytica. Facebook was allegedly told it was for a research project, not to be monetized and given to a firm.

The app may have harvested as many as 87 million Facebook users’ data, although the numbers are unclear.

Sen. Amy Klobuchar (D-MN) tried to draw a link between Cambridge Analytica and Trump’s win, asking what states those potentially targeted lived in.

Zuckerberg said he did not have the information with him, but he could follow up with her office.

“OK, because as we know, that election was close, and it was only thousands of votes in certain states,” she said.

Zuckerberg also said Facebook is also investigating whether there is a link between those targeted by Cambridge Analytica and those who were potentially exposed to Russian political ads.

Klobuchar also asked whether those whose data was collected by Cambridge Analytica were the same ones who were potentially exposed during the election to Facebook pages associated with the Internet Research Agency, a Russian company running influence operations.

“Senator, we’re investigating that now. We believe that it is entirely possible that there will be a connection there,” he said.

This article has been updated.