The files will include the case in which Mr. Ivory testified: the 1995 death of his 4-year-old cousin, Shamone Johnson, who skated into a barrage of bullets that was meant for a local gang at the Prospect Plaza housing project in Brooklyn. The investigators who visited Mr. Ivory in the last few weeks wanted to know if he stood by information he gave when he identified a man accused of the shooting. At the time, Mr. Ivory said he recognized a photograph of the suspect.

Now Mr. Ivory, 40, says that was not true. “I didn’t recognize anyone,” Mr. Ivory told The New York Times in a telephone interview from Eastern Correctional Facility, a prison in Ulster County where he is serving time in an unrelated homicide. “The cops would say the number out loud and say, ‘Take a good look at it,’ so I went with it. I thought they knew what they were doing. And I figured if it wasn’t him, he could beat it at trial.”

Image Sundhe Moses was sentenced in Shamone's death. He said he signed a confession only after physical abuse by Louis Scarcella. Credit... New York Corrections Department

Mr. Ivory said the prosecutor who visited him in prison several weeks ago casually mentioned that he could face perjury charges if he changed the story he had testified to be true.

Records show that it was not Mr. Scarcella who presented the photographs to Mr. Ivory. His role in the case involved obtaining the confession, which the defendant, Sundhe Moses, said he signed only because the detective had become physically abusive. When it came time to testify in court, Mr. Ivory ultimately did not identify Mr. Moses, but the jury, apparently persuaded by the confession, voted to convict.

Mr. Moses was sentenced to 16 years to life for Shamone’s death.

“I feel bad,” Mr. Ivory said. “I wouldn’t want somebody to be in jail for something they didn’t do.”

Mr. Hynes would not comment on the investigation, nor would he reveal which cases are being reviewed. But interviews with lawyers and witnesses involved in many of Mr. Scarcella’s cases, and who would presumably be central to any review, have provided a general portrait of the investigation’s current status. While some witnesses say they have indeed been contacted, far more say they have not been.