This weekend marks the 20th anniversary of the 9/11 terror attacks, which claimed the lives of nearly 3,000 people on that day alone.

But two decades later, the death toll continues to mount for emergency responders who rushed to the front line of tragedy and breathed in the toxins at ground zero in the weeks that followed.

News 12's senior investigative reporter Tara Rosenblum has been following their escalating health struggles for 15 years and provides a look at where some of them are today.

When the Twin Towers crumbled on Sept. 11, 2001, nearly 90,000 emergency responders raced to the front lines of the unfolding tragedy.

They were hoping to save lives - thinking little of their own - because they were told they didn't have to. They were also told by a former EPA administrator a week later that the air was safe to breathe and the water safe to drink.

They breathed in the air at ground zero for months, using little more than paper towels or, in some cases, just their hands, as masks to clear away the nearly 2 million tons of toxic debris.

Two decades later, the bill is coming due because that air wasn't safe to breathe.

The World Trade Center dust is taking a terrible toll on 9/11 heroes - many of their once-healthy bodies are now ravaged by 9/11-linked illnesses.

Former NYPD Lt. David Chong, now the White Plains police commissioner, is one of those heroes. He was inside the South Tower fighting to save lives when the floor underneath him split in half.

Twenty years later, he is fighting pancreatic cancer.

Commissioner Chong is far from alone. He is one of almost 15,000 9/11 responders who are battling cancer, according to new data released by health officials to the Turn to Tara team.

Another 40,000 ground zero workers suffer from chronic ailments at rates higher than the general population, ranging from heart disease to serious upper-respiratory issues. But 4,000 of them are no longer here to share their stories, including former Marine and Peekskill Detective Charlie Wassel.

News 12 reported on Wassel's heroic health battle - and his subsequent death - back in 2013. Wassel died still waiting for benefits from the 9/11 Victim Compensation Fund.

Retired NYPD officer-turned-attorney Matt McCauley was a driving force behind the federal legislation, and now he is on a different mission: to ensure the legacy of his fallen comrades lives on.

Two large stone monoliths will be unveiled this week at The Rising in Westchester County this week, etched with the names of the local responders who died from exposure to World Trade Center toxins.

Dr. Michael Crane, the medical director of the World Trade Center Health Program at Mount Sinai, says as bad as it's been, he fears the worst is yet to come.

"It's going to get harder. There's going to be more conditions," he says.  "Asbestos is known to produce two types of cancers - it usually starts at the 20-year mark."

This means the tragedy of 9/11 will continue to take its toll for decades - not just on the bodies of these heroes, but their minds as well.

Commissioner Chong knows that struggle himself all too well. His goal now is to keep his name off of the memorial for as long as he can so he can honor the sacrifices of the tens of thousands of men and women.

"Each one of these persons is a soul and represents the soul of America," he says.