The announcement came days before the 25th anniversary of the terrorist attacks on the World Trade Center, when the 2,977 victims will be honoured.
But questions about the toxic air after the two skyscrapers collapsed have continued to cloud the memory. More than 9,400 people have died from injuries believed to be linked, among other things, to exposure to pollution after the attacks.
"These are documents that show that the city knew about the toxic air around Ground Zero, when it knew about it, and how it acted to limit liability," Mamdani said at the press conference where he announced that the documents were being made public digitally.
