The district attorney’s office has so far refused to release a full list of cases under review and declined to discuss particular ones. In addition, it is unclear what individual prosecutors knew about Mr. Scarcella and the accusations against him. But the potential problems seen in a sampling of cases in which Mr. Scarcella testified raises the prospect that innocent people may be serving life sentences for crimes they did not commit, or that guilty people whose cases were compromised could go free.

That 1997 murder case in which the prosecutor rose to defend Mr. Scarcella was emblematic of flaws in the detective’s cases: contradictory witnesses, disputed confessions and prosecutors willing to accept his findings and take them to trial.

Jabbar Washington, who is serving 25 years to life, was convicted of taking part in a home invasion in 1995 that left one person dead and two others seriously injured. The case against him was built around his own confession and the testimony of a woman who said she saw the crime, but there were reasons to be skeptical of both.

Mr. Washington claimed the detective had told him what to say and then beat him until he confessed. The district attorney’s office accepted the confession, which had been videotaped, even though it started with the same two sentences uttered by suspects Mr. Scarcella had interrogated in other cases. Mr. Reeves, who defended the detective’s honesty during his closing argument, declined to comment.

The lead witness told Mr. Scarcella she could identify the killer, who had worn a mask, but she was unable to do so at trial. In response to an appeal years later, an assistant district attorney, Marie-Claude P. Wrenn-Myers, acknowledged that the witness had been “equivocal and somewhat inarticulate.”

“But,” she added, “the jury could consider Detective Scarcella’s testimony in tandem with hers.”

Critics, including political opponents, defense lawyers and inmates, have questioned the propriety of Mr. Hynes leading the investigation into his office’s work, particularly because most of the cases under review were prosecuted on his watch. (The district attorney’s office said 10 of the cases were closed under Elizabeth Holtzman, who was district attorney before Mr. Hynes took office in 1990, but his office defended them if they were appealed.)