“The thought that for some women and some children, their homes had become a place where they confronted the most violence and where they felt the most unsafe,” Ms. Singas said in a recent interview about her motivation for prosecuting cases involving victims of domestic violence. “I felt I wanted to do everything I could to make those peoples lives better and to hold their offenders accountable.”

Ms. Singas also served as the lead prosecutor on a panel created in 2010 by her predecessor, Kathleen Rice, who is now a congresswoman, to review the conviction of Jesse Friedman, who pleaded guilty in 1988 to charges he had sexually abused children along with his father, Arnold, who ran computer classes in the basement of their Great Neck, N.Y., home. After Mr. Friedman was freed on parole in 2001, he said he was innocent, and contested his conviction in the courts. The United States Court of Appeals ruled in 2010 that it could not overturn Mr. Friedman’s conviction because the appeal was too late, but that there was a “reasonable likelihood” that he was wrongfully convicted.

After a three-year review, the panel led by Ms. Singas stood by the conviction, though in 2013, one of the alleged victims wrote a letter to the Nassau County district attorney’s office recanting his statements. He said the Friedmans had never sexually assaulted him. He was reportedly one of several victims to change or dispute parts of accusations attributed to them in the case.

Mr. Friedman is fighting in court with the district attorney’s office for access to evidence in the case.

His lawyer, Ronald Kuby, said Ms. Singas is “a prosecutor who has spent a lot of time prosecuting child sex abuse and domestic violence cases. Her bias is to assume that every alleged victim is truthful.”

“You believe you’re on the side of the angels,” he said. Still, he said Ms. Singas was ideally suited to investigating Mr. Schneiderman and he described her as “fair, aggressive and smart.”

It is rare for a governor to appoint a special prosecutor, and it can drag a criminal case into the world of politics. In 1996, Gov. George E. Pataki removed Robert T. Johnson, then the Bronx district attorney, from a case involving a slain police officer because he believed Mr. Johnson would not seek the death penalty. Mr. Johnson objected to the decision, fought the matter in court and lost. In 1986, Gov. Mario Cuomo appointed a special prosecutor to investigate the racially charged attack of three black men in Howard Beach after lawyers for the men accused the Queens district attorney of covering up aspects of the assault.