WASHINGTON - Senate officials said Monday that they cannot legally release any potential records related to a complaint purportedly filed by a former aide to Joe Biden who has since accused him of sexual misconduct, rebuffing a request by the presumptive Democratic presidential nominee. 

Tara Reade has accused Biden, who was then a senator from Delaware, of sexually assaulting her in 1993, although she has said a formal complaint she filed that year describes only harassment, not assault. Biden, who denies all the allegations, has responded in part by calling on the Senate to release all the documentation pertaining to the complaint that Reade says she filed.

Responding to a letter Biden sent Friday, the secretary of the Senate's office, on the advice of legal counsel, concluded that the "Secretary has no discretion to disclose any such information as requested." The office, which did not confirm or deny the complaint's existence, based its decision in part on a review of confidentiality requirements.

The letter from Biden was related to Reade's allegation that Biden reached up her skirt and penetrated her with his fingers in 1993. Biden unequivocally denied the allegations on Friday, speaking directly about them for the first time. He also said he did not recall any complaint being filed.

Reade has told The Washington Post that her complaint dealt with harassment in the office, not assault. She has said that she cannot recall the office to which she filed her complaint and that she does not have a copy.

Reade was employed in Biden's Senate office for nine months, ending in 1993. She said she filed a complaint that year with a congressional human resources or personnel office. The Senate Office of Fair Employment Practices fielded complaints starting in 1992.

On Friday, Biden said relevant documents would not be found in his Senate papers, which are closed to the public, but would rather be housed at the National Archives.

A spokesperson for the Archives said that it has no control over the release of such records and that any documents "would have remained under the control of the Senate." A Senate resolution requires that such personnel records remain out of public view for 50 years.

On Friday afternoon, Biden's campaign released a copy of a letter the candidate had sent to the secretary of the Senate.

"The Archives now states that the records would have remained under the control of the Senate. Accordingly, I request that you take or direct whatever steps are necessary to establish the location of the records of this Office, and once they have been located, to direct a search for the alleged complaint and to make public the results of this search," Biden wrote.

He added, "I would ask that the public release include not only a complaint if one exists, but any and all other documents in the records that relate to the allegation."

The latest development adds to the fog surrounding the Reade allegations and illustrates the difficulty of looking into a 27-year-old alleged incident.

After the secretary of the Senate's statement, Biden campaign attorney Bob Bauer responded with follow-up questions about the possibility for a more limited release.

"Is just the existence of any such records subject to the same prohibition on disclosure?" Bauer asked, according to a statement from the campaign.

Without naming Reade, he asked if the accuser might be able to obtain the records: "Is there anyone, such as a complainant, to whom such records, if they exist, could be lawfully disclosed?" Finally, Bauer asked whether the Senate could release "the procedures and related materials" in 1993 for processing a complaint such as the one Reade has described.

The secretary of the Senate's office responded late Monday to say it was advised by legal counsel that even disclosing the existence of such records "would amount to a prohibited disclosure under the Government Employee Rights Act of 1991." The office said it was not aware of any exceptions in the law allowing it to disclose any records, "even to original participants in a matter."

In response to the campaign's third question, the office attached a public document from the time of the alleged complaint titled "Office of Senate Fair Employment Practices" - the entity that Bauer referred to in his question and that the secretary of the Senate's office referenced in its initial response to Biden.

The document outlines the procedure for bringing concerns to the attention of that office. It states that an employee would first submit a request for counseling to the director of the Office of Senate Fair Employment Practices, in person, by phone or in writing. Unless the employee and the director agreed in writing to contact the employee's office, the information relating to the counseling would not be disclosed to anyone outside the Office of Senate Fair Employment Practices, the document states. If the matter were not resolved, the employee could request mediation, at which point the employee's office would be contacted and involved, the document says. If the matter still remained unresolved after mediation, an employee could file a "formal complaint," according to the document.

Reade did not immediately reply to a request for comment.

Over 35 months, which covered Reade's employment period, 479 people sought assistance from the Senate fair employment office, according to congressional testimony in 1995.

Of those, 325 sought informal advice, while 102 went into a five-step process that included counseling and mediation. Only 38 people ended up filing a formal complaint.

If Reade was among those who filed a formal complaint, her record would not normally be available until 2043, based on a Senate resolution passed in 1980 mandating that such information remain private for 50 years.

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The Washington Post's Seung Min Kim contributed to this report.