New York City released over 170,000 pages of documents revealing officials repeatedly misled residents about the toxic air quality levels after the September 11, 2001, attack on the World Trade Center, just days before the city marks its 25th anniversary.

The disclosure reveals the scale of lives lost and harms for those whose health was affected in the years since the tragedy. It’s also expected to give the public a better understanding of how the city responded following the collapse of the towers as they raced to restabilize and reopen Lower Manhattan.

Those living near Ground Zero were repeatedly reassured by officials that the air was safe, despite internal data and residents’ experiences that contradicted their claims, according to the documents.

The documents might only contain a fraction of the air quality reports taken at Ground Zero, but they also include crucial internal memos.

In some of them, officials raised alarms regarding environmental testing between October and November 2001, which regularly detected elevated levels of toxins, including asbestos and hard-to-detect, dangerous chemicals.