Sam Kellner is a man twice shunned and living in a deepening shadow.

Five years ago, this gray-bearded and excitable man with a black velvet yarmulke spoke out about the sexual abuse of his 16-year-old son by a prominent Hasidic cantor. As Mr. Kellner helped investigators with the Brooklyn district attorney’s office search for other young Orthodox victims of this man, the Orthodox establishment grew ever angrier at him. The rabbi at his Hasidic synagogue in Borough Park, Brooklyn, denounced Mr. Kellner as a traitor and forbade parishioners to talk with him on the street. Yeshivas barred his sons. His businesses dried up — he pawned his silverware to meet his bills. And he still fears that he will never find a marriage match for his son.

“I felt murdered and abandoned,” Mr. Kellner said. “I’m ruined.”

This, however, was a prologue to a worse situation. In April 2011, after the district attorney’s office gained a conviction against that cantor, Baruch Lebovits, the prosecutors turned around and obtained an indictment of Mr. Kellner. They said, based on a secret tape and the grand jury testimony of a prominent Satmar supporter of Mr. Lebovits, that he had tried to extort hundreds of thousands of dollars from Mr. Lebovits.

District Attorney Charles J. Hynes has shown great deference to the politically powerful Hasidic community over the years, and it has rewarded him with large margins on election days. Even his heralded crackdown on Hasidic sexual abuse was a velvet glove wrapped around a velvet fist, as he took the unusual step of refusing to publicize the names of defendants — even the convicted.

Mr. Hynes extended no such courtesy to Mr. Kellner. “We allege that Kellner sent emissaries to Lebovits’s family telling them that he controlled the witnesses against Baruch Lebovits,” the district attorney said at a 2011 news conference, “and that in return for $400,000, he would ensure that the witnesses would not testify.”