New York City has released more than 170,000 pages of documents revealing that city authorities were aware of dangerous air quality around Ground Zero after the September 11, 2001 attacks, even as officials repeatedly told the public the air was safe to breathe. Mayor Zohran Mamdani announced the release at a news conference on Tuesday, stating plainly: "People got sick because the leaders they trusted lied and told them they were safe to breathe in toxic air."

The documents — including air-quality reports, internal memos, and communications among city officials — were made public through an online portal as part of a legal settlement with 9/11 Health Watch, a victims' advocacy group that had taken the city to court to compel disclosure. Among the most significant records is an October 2001 memo, known as the "Harding Memo", in which a city aide warned former Deputy Mayor Robert Harding that New York could face up to 35,000 legal claims over its handling of the crisis. The document explicitly notes that the city risked being sued because its health advisories had encouraged people to return to the affected area too soon, causing toxic exposure. Asbestos, a hazardous material that can only legally be removed by licensed professionals, was detected near Ground Zero for months after the attacks, yet residents were advised to clean up dust with wet mops and rags.

The files could implicate two former New York mayors: Rudy Giuliani, who was in office at the time of the attacks, and Michael Bloomberg, who served from January 2002 to December 2013. Benjamin Chevat, director of 9/11 Health Watch, said four successive mayoral administrations had withheld the documents from the public, Congress, and the City Council. Giuliani's spokesman did not respond to requests for comment, and Bloomberg's team declined to comment. TV host and 9/11 survivor advocate Jon Stewart, speaking at the news conference, noted sarcastically that officials had "only buried that information for 25 years."

The human cost of that concealment has been enormous. The attacks on September 11, 2001, in which hijackers crashed planes into the Twin Towers in Lower Manhattan, the Pentagon near Washington, and a field near Shanksville, Pennsylvania, killed 2,977 people. In the years since, more than 9,400 have died from illnesses linked to toxic exposure in the area, according to a federal medical monitoring programme, and at least 49,000 first responders and survivors have been diagnosed with cancer. Additional documents will be released in waves over the next twelve months. The release comes ahead of the 25th anniversary of the attacks this September, and advocates say the disclosures are essential to ensuring accountability and justice for those still suffering today.