New York City’s top investigative agency has tapped outside lawyers to probe what previous mayoral administrations knew about the toxic dust at Ground Zero and what if anything they did about it.

The Department of Investigation said it is entering into a contract with Epstein Becker & Green to help conduct the inquiry into the mayoral administrations from Rudy Giuliani to Mike Bloomberg, Bill de Blasio and Eric Adams.

Giuliani was the city’s mayor on 9/11 and for the three months after, while Bloomberg helmed the Big Apple during ensuing years of reconstruction.

The later de Blasio and Adams administrations were also the keeper of records that could be scrutinized.

“Services will include conducting an investigation to ascertain the knowledge possessed by mayoral administrations on environmental toxins produced by the September 11, 2001 terrorist attacks on the World Trade Center and to submit a report to the Council thereon,” the DOI said in a notice about the negotiated procurement.

The investigation is required by a City Council resolution passed in July 2025, with the DOI also ordered to receive $3.81 million over a two-year period for the fact-finding probe.

Environmental activists have long claimed that city officials misled the public about toxic air risks after 9/11.

Just days before the 25th anniversary of the 9/11 attacks, the Mamdani administration released nearly 170,000 pages of records detailing health and air-quality concerns — including a bombshell October 2001 memo showing city officials knew about potential Ground Zero health risks.

Those records are now publicly available in an online portal.

Michael Barasch, whose Barasch & McGarry law firm represents 50,000 people in the World Trade Center Health program, said he does not believe the probe will open the legal floodgates against the city.

He noted that the US Environmental Protection Agency declared the air safe Sept. 18, 2001 — a week after the attacks, providing the city legal cover.

But he said the exploding number of patients sickened by 9/11-related illnesses still want to know who knew what and when.

“I don’t think Mayors Giuliani and Bloomberg knew the air was unsafe. They went back to work,” Barasch said.

“I don’t think the mayors knew — but the [city] Law Department knew. Why did they hide the information that the air was unsafe?” he said.

The top plaintiff lawyer said the secretiveness extended through four administrations.

Barasch said he himself returned to work at his downtown office when authorities declared the air safe to breathe.

“The air reeked,” he said.

He applauded Mamdani for opening the files.