For nearly a quarter century, New Yorkers, Ground Zero workers, advocates and elected officials have called on City Hall to reveal the truth about what it knew about the air quality in downtown Manhattan after the 9/11 attacks.

On Tuesday, Mayor Zohran Mamdani released tens of thousands of long-guarded city documents related to the air quality that showed how first responders who rushed to the World Trade Center were likely exposed to dangerous toxins.

The mayor’s office released the first 170,000 pages of records via an online portal. It includes memos from city leaders and agencies going as far back as the Giuliani administration, which ran from 1994 to 2001.

Mamdani, who was joined by 9/11 responders and advocates at City Hall, said that New Yorkers needed to know the truth.

“People got sick because the leaders they trusted lied and told them they were safe to breathe in toxic air,” he said. 

“9/11 Tribute in Light: Live from Lower Manhattan,” a one-hour ABC News multiplatform live special, premieres on Friday, Sept. 11, at 8:00 p.m. EDT across ABC, Disney+, Hulu, National Geographic, ABC Owned Television Stations livestreams and ABC News Live.

“We are here to release these documents today because for a long time New Yorkers have known the truth, but they have been unable to see the truth in any document presented to them,” he added.

Among the documents that have been revealed is the “Harding Memo”, an October 2001 memo from then-Deputy Mayor Robert Harding that indicated the city knew of the air quality dangers and the legal liability even through publicly the city declared the air was safe.

The memo has been sought by 9/11 victims advocates for decades.

Another released document shows the presence of asbestos on the facade ledge of 15 John Street, away from Ground Zero, months after the attacks, in July 2002.

In addition to releasing the first throve of city documents, the city announced a settlement of two lawsuits brought by the advocacy group 9/11 Health Watch, which sued the city to force publication of the records.

Nearly 6,000 people have died of 9/11 related illnesses since the attacks and many are suffering from chronic illnesses, according to the group.

Advocacy groups filed several Freedom of Information Act requests for the documents over the years, but it was only last year that 68 boxes of records were found in a city office, according to city officials. 

“The Daily Show” host Jon Stewart, who has been advocating for health benefits for 9/11 first responders, said at the news conference that many of those victims had to fight for the documents while they were “sick and dying.”

“I’m not saying the information may have changed the outcomes, unfortunately, for their families, but I guarantee you it would not have been the struggle that it was to get people to recognize what they all knew … that there was poison in the air,” he said.

Mamdani declined to directly blame any of his predecessors, saying he would “leave that to New Yorkers,” but said, “administration after administration has ignored those calling for answers and clarity.”

The mayor said that the city will continue to use its resources to promote two federal programs established under the Zadroga Act: the World Trade Center Health Program and the September 11th Victim Compensation Fund. They are designed to provide relief to residents and workers who were in downtown Manhattan after the attacks if they experience any related illnesses.