In a new development of the already contentious Supreme Court confirmation process, nominee Judge Brett M. Kavanaugh has been accused of attempted sexual assault from years ago, while he was still in high school.

The allegation was revealed in a letter to Sen. Dianne Feinstein (D-Calif.) earlier this summer, but the senator did not reveal the details of it until Wednesday, when she turned the letter over to the FBI.

Feinstein announced on Thursday, “I have received information from an individual concerning the nomination of Brett Kavanaugh to the Supreme Court. That individual strongly requested confidentiality, declined to come forward or press the matter further, and I have honored that decision. I have, however, referred the matter to federal investigative authorities.”

The FBI, which is responsible for background research on judicial nominees and other presidential appointments, said in a statement that it had included the information in Kavanaugh’s background file after receiving it from Feinstein on September 12, but would not be investigating the 35-year-old claims.

Details of the allegations first came out in The New Yorker in a piece by Ronan Farrow and Jane Mayer, who wrote, in part; “The allegation dates back to the early 1980s, when Kavanaugh was a high school student at Georgetown Preparatory School, in Bethesda, Maryland, and the woman attended a nearby high school.”

“In the letter, the woman alleged that, during an encounter at a party, Kavanaugh held her down, and that he attempted to force himself on her,” their article continued. “She claimed in the letter that Kavanaugh and a classmate of his, both of whom had been drinking, turned up music that was playing in the room to conceal the sound of her protests, and that Kavanaugh covered her mouth with his hand.”

“Not until the eve of his confirmation has Sen. Feinstein or anyone raised the specter of new ‘information’ about him.”

“She was able to free herself. Although the alleged incident took place decades ago and the three individuals involved were minors, the woman said that the memory had been a source of ongoing distress for her, and that she had sought psychological treatment as a result.”

Judge Kavanaugh, married and a father of two daughters, swiftly addressed the claims.

“I categorically and unequivocally deny this allegation. I did not do this back in high school or at any time.”

The classmate named in the letter denied the account as well.

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Related: Kavanaugh Chaos: New Allegations Released by Feinstein in a Letter

Several Democratic senators are calling for the confirmation hearings to be put on hold while the matter can be investigated thoroughly, but Sen. Chuck Grassley (R-Iowa), chair of the Senate Judiciary Committee, said the confirmation would move forward as previously planned.

His office also released a letter from 65 women who knew the nominee at the time and throughout his career — and said that it did not fit their experience with Kavanaugh at all.

White House spokesperson Kerri Kupec indicated the administration believes this is simply an attempt to delay the nomination, saying, “Not until the eve of his confirmation has Sen. Feinstein or anyone raised the specter of new ‘information’ about him.”

While the Senate Judiciary Committee has held several sessions of questioning for Kavanaugh, both openly and behind closed doors, there is no indication Feinstein had referred to the letter before this week.

This article has been updated.