Neither Mr. Stryk nor any other American consultant is listed as having registered with the Justice Department to represent Prince Andrew, which could be required under the Foreign Agents Registration Act if a consulting arrangement had been reached involving lobbying or public relations.
Blackfords has been representing Prince Andrew, the Duke of York, in a contentious back-and-forth with federal prosecutors in New York who are investigating allegations of sex trafficking and other crimes by Mr. Epstein and his associates.
Prince Andrew, 60, has not been charged in the case.
But in August, Virginia Roberts Giuffre accused the prince of having sex with her three times when she was 17 years old after she was connected to him by Mr. Epstein.
The prince denied her claim in an interview with the BBC in August and sought to minimize his long friendship with Mr. Epstein, who killed himself last summer at a federal jail in Manhattan while awaiting trial on sex trafficking and conspiracy charges. He had met Mr. Epstein through Ghislaine Maxwell, a British socialite and Mr. Epstein’s onetime girlfriend, who was arrested on Thursday and charged with luring multiple underage girls into Mr. Epstein’s orbit.
Prince Andrew had indicated a willingness to help American law enforcement officials with their investigations late last year. But since then, prosecutors in New York have publicly criticized him on multiple occasions for offering “zero cooperation” and for stonewalling.