In an interview last fall, Cyrus R. Vance Jr., the Manhattan district attorney, and his chief assistant defended their decision to strike a plea deal in 2016 that allowed a gynecologist accused of sexually abusing 19 patients to avoid going to prison.

The chief assistant, Karen Friedman Agnifilo, said the case against the doctor, Robert A. Hadden, was “not a slam-dunk.” Among other things, she said, some of the women were pregnant when they say the assaults occurred and so they could not see what was happening. That, she said, could have been used by the defense to undermine them as witnesses.