Senate Judiciary Chairman Lindsey Graham has started deposing witnesses in his committee’s investigation into abuse of the Foreign Intelligence Surveillance Act during the 2016 election.

The South Carolina Republican told reporters on Tuesday that he had begun conducting closed-door depositions but did not elaborate on the state of the investigation, according to the Hill. Graham requested closed-door interviews with 17 Department of Justice and FBI officials last month.

In a Feb. 12 interview with CBS News, Graham said that depositions would begin sometime in late February or early March and said that the proceedings could last for weeks.

Graham has led the push to investigate current and former DOJ and FBI officials for abuses uncovered by DOJ Inspector General Michael Horowitz in a December report. Horowitz’s inquiry about the Justice Department’s 2016 investigation into the Trump campaign discovered at least 17 "significant errors and omissions" in FISA applications submitted by DOJ and FBI officials.

The Justice Department opened an investigation into then-Trump campaign adviser Carter Page over suspected ties to Russian agents and an alleged plot to coordinate with Russia to influence the 2016 election. Horowitz found that the FBI investigators working on the case misled Foreign Intelligence Surveillance Court judges to get approval for at least two of the four FISA applications submitted to continue the investigation into Page.