Some of Democratic presidential candidate Hillary Clinton’s closest aides, including her longtime adviser Huma Abedin, have provided interviews to federal investigators as part of the probe into the security of Clinton’s private email server, U.S. officials briefed on the investigation told CNN on Thursday.

The investigation is still ongoing, but so far investigators haven’t found evidence to prove that Clinton willfully violated the law, the officials told the network.

Clinton’s use of a private server in her New York home for her government work is being investigated by the FBI, the State Department’s internal watchdog and several Republican-controlled congressional committees.

In February, a federal judge ruled that State Department officials and aides to Clinton should be questioned under oath about whether her private email system was an effort to skirt open records laws.

In recent weeks, multiple aides have been interviewed — some more than once, the officials told CNN.

A date for an FBI interview of Clinton has not been set, these officials said, but is expected in the coming weeks. A federal judge in Washington on Wednesday ordered that Clinton may have to testify in a lawsuit related to the private email server.

Abedin has cooperated with the probe, the officials told CNN. Lawyers for Abedin declined to comment. The officials say the interviews of Clinton and her aides would be a routine part of an investigation like this.

The probe remains focused on the security of the server and the handling of classified information and hasn’t expanded to other matters, the officials said. Spokesmen for the FBI and Justice Department declined to comment.

The Clinton campaign has not yet responded to CNN’s request for comment. David Kendall, an attorney for Clinton, had no comment.

Clinton has said she used private emails out of “convenience”, though she has also admitted it “would have been better” to have two accounts to separate work and personal emails.

She has apologized for the use of a private email server, even though she had insisted she didn’t need to apologize because “what I did was allowed.”

While Clinton has denied that she sent or received classified emails from her private server, it was revealed recently that some of her mails were beyond “top secret”.