Both men have denied the allegations, and Dershowitz is threatening to initiate disbarment proceedings against Cassell and Bradley Edwards, a Florida attorney who also represents Jane Doe #3, according to The Wall Street Journal.
Dershowitz told the newspaper that he is an "innocent victim of an extortion conspiracy" and said the sex claims are a "completely, totally fabricated, made-up story."
Cassell, a former federal judge in Utah and longtime advocate of victims' rights, and Edwards released a statement saying that "out of respect for the court's desire to keep this case from being litigated in the press, we are not going to respond at this time to specific claims of indignation by anyone."
The two attorneys did say their allegations are factual and had been carefully investigated before they were filed.
"We have also tried to depose Mr. Dershowitz on these subjects, although he has avoided those deposition requests," their statement says. "Nevertheless, we would be pleased to consider any sworn testimony and documentary evidence Mr. Dershowitz would like to provide which he contends would refute any of our allegations."
The Associated Press reported that royal officials on Friday denied that Andrew, 54, also known as the Duke of York, engaged in any "impropriety with underage minors."
"This relates to longstanding and ongoing civil proceedings in the United States, to which the Duke of York is not a party," Buckingham Palace said in a written statement. "As such we would not comment on the detail."
According to The Associated Press, the statement added: "However, for the avoidance of doubt, any suggestion of impropriety with underage minors is categorically untrue."
The controversy stems from a 2008 petition filed by two women in U.S. District Court in West Palm Beach that alleges violations of the federal Crime Victims' Rights Act (CVRA) in the prosecution of Epstein. The two — called Jane Doe #1 and Jane Doe #2 — allege they had been child victims of sex-trafficking crimes committed by Epstein and had the right under the CVRA to confer with prosecutors, to be heard at public proceedings regarding any plea or sentence, to receive restitution and to be treated with fairness.
Instead, they allege, the government secretly negotiated an agreement that precluded any federal prosecution in the case. Epstein pleaded guilty in state court in Florida to two counts of solicitation of prostitution involving a minor and served 13 months in prison before being released in 2009.
The alleged victims want the plea deal rescinded.
Cassell's motion seeks to add to the suit two more alleged victims who say their rights were violated: Jane Doe #3, who was 15 when she became a victim of the sex-trafficking scheme in 1999, and Jane Doe #4, who was 16 in 2002 when she became involved. The two were repeatedly sexually abused by Epstein, according to their court filing.
The motion alleges Epstein also trafficked Jane Doe #3 to ingratiate himself with powerful people for political and financial gain, as well as to obtain potential blackmail information. It claims one of those people was Dershowitz, a close friend of Epstein, who later helped negotiate the agreement that provided immunity from federal prosecution in the Southern District of Florida to Epstein and potential co-conspirators — including Dershowitz himself.
According to the motion, Jane Doe #3 was kept as a sex slave from about 1999 through 2002, when she managed to escape to a foreign country and hide out.
In a statement released by her attorneys, Jane Doe #3 said she is looking forward to vindicating her rights as an innocent victim, despite the attacks on her allegations.
"It appears that I am now being unjustly victimized again," she said. "These types of aggressive attacks on me are exactly the reason why sexual abuse victims typically remain silent and the reason why I did for a long time. That trend should change. I'm not going to be bullied back into silence."