NEW YORK (CBSNewYork) – Thousands of first responders have developed life-threatening illnesses related to the weeks they spent in the rubble of the twin towers.

Born out of that tragedy, the Stephen Siller Tunnel to Towers Foundation provides support for first responders and their families.

Stephen Siller died in the Sept. 11 terror attacks (Credit: CBS 2)

Frank Siller and his family founded the nonprofit after his brother, Stephen, an off-duty New York City firefighter, was killed while responding to the World Trade Center on 9/11.

Siller had just gotten off his shift in Brooklyn. When he heard the news, he called his wife to tell her he would be late because he had to help those in need.

He never returned.

Frank Siller spoke about his brother and what this day means to his entire family.

“It’s the day we lost our little brother, you know. Stephen was the youngest of seven kids but, he was so much younger than… I was closest in age, I was 14 years older than my brother Russ who was 25 years older than him,” Frank said. “My parents died when he was a little boy. We raised him, he was like a son to us as well as a brother. He always wanted to be a firefighter, he loved serving people and he paid the ultimate sacrifice 18 years ago today.”

“I remember him questioning once why he was put on this earth, why was I even born and I said ‘Stephen, you know your brothers and sisters will always be there for you and someday you’ll do something very special.’ And I didn’t know it was going to be this, by any means, that he ran through a tunnel and because of that act, I think he’s changed a lot of lives. Not many of us could say that – he has,” Frank added.

On the last Sunday in September, runners and walkers retrace Stephen Siller’s steps from Brooklyn, through the Battery Tunnel, and into Lower Manhattan in the Tunnel to Towers run.