FDNY union leaders slammed the city Monday for the discovery of 68 boxes of ground zero toxin records.

They say records were turned over by city officials as part of ongoing litigation, claiming that "City of New York and the DEP secretly maintained 68 boxes of Ground Zero toxin records while publicly denying their existence for decades."

"New York City firefighters demand to know who in the New York City government hid those documents all the way back in the beginning and continued to keep those documents held all these years," said Andrew Ansbro, of the Uniformed Firefighters Association of Greater New York.

Lawyers from Turken, Heath and McCauley tell News 12 they were given a chance to review records, and while they were not told how they were assembled or where they were stored, they are now being sorted into two categories: asbestos, and non-asbestos-related.

"What stuck out to us was the earliest mention of asbestos, in these documents, dates back to September of 2011," said attorney and former first responder Mathew McCauley.

The revelation came as a betrayal for 9/11 first responder families, who fought for years to prove their loved ones died from 9/11-related illnesses.

Jennifer McNamara, the widow of John J. McNamara, of Engine 243 in Crown Heights, tells News 12 her husband spent over 500 hours at ground zero, between responding on the day of the attacks and subsequent cleanup.

He died of colon cancer in 2009, and she says for years, the city denied his time in ground zero was a factor.

In September, the Daily News reported that "city lawyers" found records to share "about the dangers of the 9/11 toxins swirling around Ground Zero" after denying their existence for more than two decades.

"Did they throw these in a big pile and forget to tell anybody?" she said. "To think that this could have happened sooner, that he could have known about it, going to his death, is very upsetting."

While John died prior to the passage of the first 9/11 first responder support bill, advocates say many conditions are still not included in the federal guidelines that help first responders afford their treatments.

9/11 advocate John Feal, who frequently lobbies in Washington for first responders' bills, hopes the boxes can have the proof the government needs to begin covering neurological, immune and heart problems that he says many first responders face.

"It would help so many people who are excluded from this piece of legislation right now. Innocent lives have been taken that could have been saved, shame on them," he said.

A City Hall spokesperson responded to News 12's request for a comment: "While we cannot comment on the specifics of pending litigation, the city has begun turning over documents to plaintiff's counsel, and both parties are working out a schedule to continue this process. We remain dedicated to getting 9/11 victims and their families the answers they need, and thank the brave men and women who risk their lives every day to keep our city safe."

However, McNamara says the time for answers was over 20 years ago, when more of those heroes were still alive.

According to the AP over 6,000 first responders have gotten ill from 9/11-related diseases.