On a cold January morning in 2010, a 22-year-old woman was walking to work on 125th Street when a man grabbed her from behind, pulled her scarf across her face and yanked her to the ground by the roadside. The attacker started rubbing her thighs and tried to force her jacket open, but she managed to escape his grasp. Later that day, she provided the police with her scarf and gloves, hoping evidence could be extracted from them to help identify the assailant.

Scientists at the Manhattan medical examiner's office — a leader in developing forensic methods to crack New York City's most difficult cases — pored over the evidence in the case and was able to pull small amounts of DNA from her clothing. After more than a year, the office reported a breakthrough: John Giuca, a 26-year-old man who had been arrested in connection with an unrelated burglary, was a match for the attacker. Mr. Giuca was found guilty of attempted rape in 2014 and sentenced to 15 years in prison. But in 2021, a judge overturned the conviction, finding that Mr. Giuca had received inadequate counsel.

Specifically, his lawyer had failed to properly challenge the DNA evidence, a move that could have exonerated his client. Now, Mr. Giuca, 42, is suing the city and the lab analysts who worked on his case, accusing the analysts of fabricating evidence. His current lawyer, Robert Gage, said it was the first time that anyone from the medical examiner's office had been sued for DNA analysis leading to a wrongful conviction. Mr. Giuca's suit claims that the evidence was fabricated as part of an established practice at the medical examiner's office in which analysts often used DNA samples that were too small and complex to be reliable, and conflicting interpretations of the data were pushed aside.

Flawed results were then presented to law enforcement agencies — and then juries — as evidence of guilt, according to the lawsuit. The suit, which was filed in Federal District Court in Manhattan on Wednesday, comes more than a decade after the medical examiner's office launched an internal investigation into whether it had mishandled DNA evidence in hundreds of rape cases. A subsequent report from the state inspector general found a troubling pattern of errors at the office.

Disputes among lab analysts were papered over, and technicians often presented subjective, flawed interpretations as scientific findings to prosecutors or defense lawyers. Julie Bolcer, a spokeswoman for the medical examiner's office, said that it "operates in accordance with best practices and stands by the science produced by the experts who staff it." At the time of the attack of the 22-year-old woman in 2010, Mr. Giuca was working as a maintenance worker at a Y. M.

C. A. on 14th Street, he said in an interview. In May of the following year, he was arrested in connection with a burglary, and his DNA was entered into a state database.

The medical examiner's office, according to the lawsuit, then significantly altered the DNA profile of the attacker "to match a known profile that had been entered into the national, state or local databases." According to the lawsuit, Dr. Theresa Caragine, a senior scientist at the lab, and Dr. Kevin O'Connor, an analyst, changed results from DNA testing so that they would more closely match Mr. Giuca's profile. Dr. Caragine and Dr. O'Connor are both named as defendants in the lawsuit. Dr. Caragine did not respond to a request for comment. The medical examiner's office declined to make Dr. O'Connor, now its director of forensic biology, available for an interview. In August 2012, Mr. Giuca was arrested and charged with attempted rape, and the DNA was the only evidence that linked him to the attack.

The victim did not identify Mr. Giuca as her attacker during a lineup. In an interview the day after the attack, according to the lawsuit, the woman identified her attacker as a Hispanic man who was about 5-foot-5; Mr. Giuca is more than 6...