NEW YORK—Juror No. 50, who’s at the center of a possible mistrial in the Ghislaine Maxwell sex-trafficking case, appeared in federal court on March 8 where he plead the Fifth Amendment—the Constitutional right to refuse to answer questions in order to avoid incriminating himself. The Honorable Alison J. Nathan, the judge who presided over the case in December, granted him immunity from prosecution with the exception of perjury. “You need to answer my questions today and you need to answer truthfully,” she instructed the juror, who chose not to disclose his actual name. Soon after the jury’s Dec. 29 guilty verdict on five of six counts of sex trafficking of a minor, Juror No. 50 stated publicly he was a victim of childhood sexual abuse and had made this known to his fellow jurors during deliberations. At the center of the issue is the questionnaire potential jurors filled out prior …