, first reported by The Salt Lake Tribune
, alleges that Chief Judge Richard W. Roberts coerced the woman into a sexual relationship while she was a 16-year-old witness in a murder case and he was the prosecutor.
Roberts sent a letter to the White House retiring from the bench on Wednesday, according to the National Law Journal
, blaming health issues.
An attorney for Roberts called the rape allegations "categorically false" and said that the judge had a consensual relationship with the woman after the trial ended.
Also on Wednesday, the Utah Attorney General's Office released the findings
of a 2014 investigation into Mitchell's claims, which concluded that there was not enough evidence to "support a criminal prosecution."
In the lawsuit, the woman, Terry Mitchell, 51, alleged that Roberts coerced her into having sex with him when she was 16. Mitchell was a key witness in a case where a white Utah man was charged with killing two African-American joggers.
Mitchell saw the killing and was injured from bullet shrapnel. She also suffered emotional harm, lawyers said.
The lawsuit alleges the incident made her "emotionally and physically isolated after the murders, leaving her extremely vulnerable to a predator who pretended to be on her side, like ... Roberts. She was the target of cruel and devastating attacks and accusations by the media, fellow students and others in the community."
Mitchell was identified by name in the lawsuit, though CNN does not usually identify the victims of sexual assault.
The lawsuit alleges that Roberts assaulted her during and after the case.
Roberts' lawyers are pushing back on the accusations.
"Roberts acknowledges that the relationship was indeed a bad lapse in judgment. However, the relationship did not occur until after the trial and had no bearing on the outcome of that trial," Roberts' lawyers wrote in a statement to CNN.
In 1981, when the alleged assault occurred, Mitchell would have been of age to consent and though there is evidence of a sexual relationship, the 2014 U.S. attorney's investigation found, there was not enough to support allegations of it being coerced.
The investigator did, however, recommend further examination of whether Roberts committed ethical violations in having an affair with a witness he questioned in court and not disclosing that to the defense.
House Oversight Committee Chairman Jason Chaffetz, a Utah Republican, issued a statement Wednesday called the allegations concerning.
"Our initial review of the allegations has caused alarm and distress over their serious nature," Chaffetz said. "The Utah Attorney General recently made the committee aware of credible evidence of misconduct by a U.S. District Court Judge."
He said his committee would work with others in the House and Senate to "ensure justice is served."