A lawyer for Lt. Gov. Justin Fairfax (D) has told a prosecutor that a witness was present at Fairfax’s sexual encounter with Meredith Watson at Duke University in 2000 and can corroborate that it was consensual.

Fairfax lawyer Barry J. Pollack has written to a prosecutor in Durham, N.C., to say that the witness — whom he did not identify — backs up Fairfax’s claim that Watson’s charge against him is “demonstrably false.”

Watson has said Fairfax sexually assaulted her when they were undergraduates at Duke. She is one of two women to make that accusation against Fairfax. He denies both claims.

The other woman, Vanessa Tyson, says he sexually assaulted her in 2004 while in Boston for the Democratic National Convention.

Fairfax has said both encounters were consensual and offered to cooperate with law enforcement investigations.

Both women have said they want to testify before the Virginia General Assembly, where Republicans have called for hearings, but Democrats have resisted, saying they think the matter should be left to law enforcement.

Watson’s attorney, Nancy Erika Smith, said Fairfax was changing his story, “and now for the first time, he implicates his buddy as a participant.” She renewed her call for a public hearing on the matter before state legislators.

“If Justin Fairfax wants the truth to come out, this secret witness should testify under oath, in public, along with Mr. Fairfax, both his victims and their witnesses,” Smith said in a written statement. “Fairfax continues to fight a public hearing tooth and nail. That says it all.”

In a letter dated July 9, Pollack wrote to Durham County District Attorney Satana Deberry that the witness was one of Fairfax’s fraternity brothers. He wrote that Fairfax was visiting the witness at the fraternity house on the Duke campus in 2000, when Watson arrived.

“The eyewitness observed Ms. Watson initiate a sexual encounter with Mr. Fairfax in the eyewitness’ room,” Pollack wrote. He said the witness “remained with Ms. Watson” after the sexual encounter, when Fairfax had left.

“The eyewitness recalls the events clearly and has shared his recollections with a number of people,” the letter says, adding that the person “can say definitively that Ms. Watson was not raped or sexually assaulted by Mr. Fairfax in any way.”

Pollack wrote that none of the group had been using drugs or alcohol, and that Watson “initiated sexual contact with Mr. Fairfax and unambiguously manifested her consent to the sexual contact that occurred.”

Fairfax spokeswoman Lauren Burke said the eyewitness has been in contact with the lieutenant governor since Watson made her allegation in February. Burke declined to identify the witness and said he has not been willing to talk to reporters.

She said she could not clarify whether that person merely witnessed the sexual encounter or says he was a participant.

A spokesperson for the Durham prosecutor did not immediately respond to a request for comment.

Through spokesman Warren Cooper, Watson’s lawyer declined to comment on the specifics of Fairfax’s claim, including whether there was a witness.

“A public hearing held by the Virginia Legislature would answer all questions,” Cooper said in an email.

Fairfax had been widely viewed as a possible future governor until the accusations came to light and cast his future in doubt. Fairfax recently stepped down from his job at a private law firm, saying he wanted to focus more fully on his role as lieutenant governor.

The firm, Morrison & Foerster, conducted an internal investigation that it said found no indications of wrongdoing on Fairfax’s part since he joined the firm last year.