In a 1992 Murder, Evidence of Flawed Justice At the end of her Wednesday shift as a cashier in a pet-supply store, Elizabeth Flores clocked out and headed across Lexington Avenue in Manhattan to a diner. There, on a tropical summer afternoon in 2013, she talked about events that took place on a winter day more than 20 years ago, near Ashford Street and Livonia Avenue in the East New York section of Brooklyn. "I'm walking down the block, and my brother Tony comes up," Ms. Flores said. Using strong language, her brother, she said, described how a drug-addicted woman who hung around on that corner had confided to him that she had implicated two men in a killing that they had nothing to do with. "He told me, "She wanted to get paid," " Ms. Flores said. Her brother and the drug addict are now dead, but records show that Ms. Flores first brought her concerns to the authorities soon after that conversation in 1992. If what Ms. Flores said is now taken seriously by officials in Brooklyn, she may well loosen another brick in an already rickety structure: the conviction of two men, Everton Wagstaffe and Reginald Connor, for the kidnapping of a 16-year-old girl, Jennifer Negron, in East New York in 1992. Ms. Negron's body was found on the street at dawn on Jan. 1, the first recorded murder of more than 2,000 in New York in 1992, one of the bloodiest years in the city's history. The sole witness against Mr. Wagstaffe and Mr. Connor was the woman from that street corner, Brunilda Capella, who supported herself with prostitution and was a regular informant for the police. Like other witnesses of that era who got cold feet before trial, she was forcibly detained by the authorities in a hotel until she testified. The investigation into the killing of the young woman is notable because it is not among the roughly 50 old murder convictions now being reviewed by a special team of prosecutors at the Brooklyn district attorney's office. All those cases were handled by a single detective, now retired, named Louis Scarcella. The investigation into the death of Ms. Negron was led by a detective from a different squad, Michael Race of the 75th Precinct. His work with another informant led to the conviction of at least three innocent people. Of 750 murder investigations that he ran, Mr. Race has said, only one was "done the correct way, A to Z." That the trajectory of work by Mr. Race so closely matches that of Mr. Scarcella suggests that the legacy of injustices from that chaotic, bloody era cannot plausibly be laid at the feet of a single detective. Other investigators, as well as prosecutors, defense lawyers, judges and jurors were willing to tolerate or leave unscrutinized what was often sloppy, frayed work. In the case of Mr. Wagstaffe and Mr. Connor, no records were kept of police interviews with other important witnesses; there was no physical evidence to support the informant's claims; one witness, a police detective's daughter, who could provide a seemingly credible alibi for Mr. Wagstaffe, was never interviewed by police, prosecutors or defense lawyers; the owner of a car supposedly used in the kidnapping said she told detectives that she had it with her at church through the night of Ms. Negron's death. There is no record of any interview of her, either, even though the car was cited as important evidence. Both Mr. Wagstaffe and Mr. Connor have maintained their innocence and, after years of fighting, were able to arrange DNA testing of every piece of physical evidence that could be found; none of it implicated them, and the DNA in hair found on the victim's body came from at least one other person. In 2001, the Brooklyn district attorney, Charles J. Hynes, replied scathingly when asked about Mr. Race's work after his retirement to exonerate two other innocent men. "Race is recovering from what he used to do," Mr. Hynes replied. Since then, Mr. Hynes has created a special unit to investigate questionable convictions. Asked this week why cases by Mr. Race, which have cost the city millions in lawsuits, were not part of the review, Mr. Hynes said no one had brought claims about him to his office. But, Mr. Hynes promised, his office "would review any claim of wrongful conviction based on any reason."