The first shock came when Mordechai Jungreis learned that his mentally disabled teenage son was being molested in a Jewish ritual bathhouse in Brooklyn. The second came after Mr. Jungreis complained, and the man accused of the abuse was arrested.

Old friends started walking stonily past him and his family on the streets of Williamsburg. Their landlord kicked them out of their apartment. Anonymous messages filled their answering machine, cursing Mr. Jungreis for turning in a fellow Jew. And, he said, the mother of a child in a wheelchair confronted Mr. Jungreis’s mother-in-law, saying the same man had molested her son, and she ‘did not report this crime, so why did your son-in-law have to?