The interview at FBI headquarters in Washington, D.C., lasted about three and a half hours, according to an aide, and comes days after former President Bill Clinton’s tarmac meeting with Attorney General Loretta Lynch caused a kerfuffle over the potential for political influence on the investigation. The interview marks a signal that the end of the investigation into the presumptive Democratic nominee is near, with the FBI and Justice Department preparing to make a recommendation on whether any charges should be brought in the coming weeks.

“Secretary Clinton gave a voluntary interview this morning about her email arrangements while she was Secretary. She is pleased to have had the opportunity to assist the Department of Justice in bringing this review to a conclusion,” Clinton spokesman Nick Merrill said in a statement. “Out of respect for the investigative process, she will not comment further on her interview.”

According to TIME’s Massimo Calabresi, 20-30 FBI agents, analysts, and technical specialists have been assigned to the investigation, which largely centers on the appearance of classified information on the email server. More than 1,000 redactions have been made to the publicly released Clinton emails over classification concerns, and several messages contained information at codeword-level classification. Clinton, after first denying that any classified information was on her account, has since maintained that all the information has been classified after the fact. Her campaign has challenged those later determinations, calling it examples of over-classification in the executive branch.

It is unclear whether Clinton, or the aides who generated the emails later marked classified, are the subjects of the investigation. A number of her top aides have been interviewed by the FBI over the course of the probe.

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Lynch, recognizing the political firestorm she set off after the meeting with former President Clinton just days before his wife would meet with agents who work for her, acknowledged Friday that it was a mistake. “The fact that the meeting that I had is now casting a shadow over how people are going to view that work is something that I take seriously, and deeply and painfully,” she said. While maintaining that she would accept the recommendations of the career Justice Department officials and FBI agents involved in the investigation, a Justice Department spokesperson made clear that Lynch, as the head of the department, would still be responsible for the final determination whether to bring any charges in the case.

A parallel civil lawsuit over the State Department’s failure to produce record from Clinton’s time at the State Department had several top Clinton campaign aides facing deposition in recent weeks. The Judicial Watch suit, which gained new life after the revelation that Clinton maintained a private email server, centers on whether the server was maintained to frustrate Freedom of Information Act requests.