Last December, as part of a filing in an ongoing lawsuit, a woman charged that Mr. Dershowitz had sex with her when she was underage. Mr. Dershowitz called the claim an “outrageous lie” and over the last year has faced fallout from the accusation.

“This is very serious,” Mr. Dershowitz said last month at his apartment in Manhattan. “It involves my life, my legacy, my career, my history, my reputation.”

As he has defended that legacy, there has been a lawsuit, a counterclaim and even an accusation of an extortion plot against the billionaire Leslie H. Wexner, the chairman of L Brands, the retail empire that includes Victoria’s Secret and Henri Bendel. It also has pitted Mr. Dershowitz against another of the nation’s most famous lawyers, David Boies, who represents his accuser….

But last December, Mr. Dershowitz was drawn into the Justice Department lawsuit in an entirely different way. In a motion filed that month, Ms. Giuffre claimed that she and Mr. Dershowitz had sex when she was a minor aboard Mr. Epstein’s plane and at the money manager’s homes in New York, New Mexico and the Virgin Islands. She also asserted that Mr. Epstein had “sexually trafficked” her to other powerful friends, including Prince Andrew, the Duke of York. Buckingham Palace rejected the claims against the prince.