NEW YORK CITY — Twenty-five years after the September 11 attacks, New York City officials continue their painstaking effort to identify nearly 3,000 people who died at the World Trade Center. Now, investigators have achieved a historic milestone.

For the first time, the Office of the Chief Medical Examiner and the NYPD Detective Bureau have used forensic investigative genetic genealogy to formally identify a 9/11 victim. The approach combines DNA analysis with genealogical research to trace family connections.

The newly identified victim was an adult woman whose family has chosen not to disclose her identity publicly. She is the 1,651st person killed in the attacks to be formally identified.

“It’s a breakthrough,” Dr. Jason Graham, the city’s chief medical examiner, told ABC News. “I’m delighted to be able to say that we’ve now applied new methods to the World Trade Center identification efforts, and we have a new identification for the first time in 25 years using new methods, forensic investigative genetic genealogy.”

A quarter-century ago, such an achievement would have been difficult to imagine because the technology and methodology needed to conduct this type of investigation were not yet available.

“The technology really wasn’t there,” said NYPD Det. Gregory Paduoano. “There’s a lot of good future with genealogy.”

Forensic investigative genetic genealogy has previously helped law enforcement resolve decades-old unidentified-person cases and other long-standing cold cases. More recently, New York City’s medical examiner’s office and police department began applying the technique to the continuing effort to identify World Trade Center victims.

“We already can see that it’s promising,” said Dr. Jennifer Odien, a forensic anthropologist in the medical examiner’s office. “Not every case is going to be able to go through genetic genealogy, but we do have DNA profiles that are not matching to our reference samples, so that’s the group right now that we’re focusing on and that hopefully is going to yield more positive results.”

Odien said investigators have identified 47 DNA profiles that could potentially be suitable for identification through genetic genealogy.

Those cases account for only a small portion of the approximately 1,100 World Trade Center victims who remain unidentified 25 years after the attacks. Despite the passage of time, the Office of the Chief Medical Examiner has maintained its commitment to continuing the search for answers for the victims’ families.

“The World Trade Center was the largest mass murder in the history of the United States, and it represents also the most complex forensic identification effort in our history,” Graham said. “And being able to apply new innovations to that identification work is a remarkable way that we can keep our commitment to the families.”