The family who founded the now-famous Tunnel 2 Towers Foundation to honor their youngest brother has dedicated their life to doing just that: raising hundreds of millions of dollars for the loved ones of wounded or fallen first responders in memory of their youngest sibling, Stephen Siller.

It has been 20 years since Siller lost his life while responding to the New York City terror attacks on Sept. 11, 2001, yet his remains are among those of the more than 1,000 people who have still not been positively identified, his older brother, Frank, told Fox News. Despite this, his family has forged ahead now more than ever to support fallen first responders in his honor.

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"It’s 20 years later. You never ever get over something like this, you just learn," Frank Siller said. "And my family, we made a conscious decision after 9/11, after we got up off the ground, literally got off the ground, when we realized Stephen wasn't coming home. And we said we all, we just want to do good."

The second tower of the World Trade Center bursts into flames after being hit by a hijacked airplane in New York in this September 11, 2001 file photograph. The Brooklyn bridge is seen in the foreground.

The second tower of the World Trade Center bursts into flames after being hit by a hijacked airplane in New York in this September 11, 2001 file photograph. The Brooklyn bridge is seen in the foreground. (REUTERS/Sara K. Schwittek/Files)

He and his five other siblings did not want to "stay in that black hole and wallow," he said. He added: "That’s not what my brother Stephen would want us to do."

"And we made a conscious decision that we're going to defeat evil by goodness. And our foundation is all about doing good for the greatest of all Americans – these great Americans that go out and serve our country or these police officers, or firefighters, first responders who protect us every day."

Stephen had joined the Fire Department of New York when he was 27 and loved "everything about it," Frank said. In the years leading up to the attack, as his family grew and he fostered his passion, "he was on top of the world." 

Stephen was 34 years old and was driving home from his overnight shift on the morning of Sept. 11 when he heard the news of a plane that had crashed into the North Tower. He abandoned the day’s plans to play golf with his brothers and instead headed toward the World Trade Center. 

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He made it to the entrance of the Brooklyn Battery Tunnel, but the roadway was closed. So instead of driving into lower Manhattan, he climbed into his roughly 60 pounds of gear and ran there. The married, proud father of five ultimately did not survive.  

"Absolute last words were, ‘I’ll see you tomorrow, bro.’ I hugged him. And that was the last time I saw him. We had lunch together the day before, on September 10," Siller recalled. 

The 9/11 attacks claimed the lives of 2,977 victims, including 343 FDNY firefighters, 23 members of the NYPD and 37 Port Authority police officers, and countless others.

The foundation has since raised $250 million, and counting, for American heroes.

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Siller spoke to Fox News as he walked in the rain through Bethlehem, Pennsylvania, or roughly 400 miles into his 537-mile journey. He was nearing the end of the Never Forget Walk, but he still had several days – and several cities –before he reached his final destination of New York City on Saturday. 

Now chairman and CEO of the Tunnel to Towers Foundation, Siller has walked through six states in as many weeks as a way to honor those who died on 9/11 through what has been named the "Never Forget Walk." He is far from alone in his efforts and has often been joined by local residents and officials.

Just during his 20-minute phone conversation with Fox News Digital, which he took during his walk, he was stopped by young boy who asked for a photograph and was greeted by a local city mayor as they discussed upcoming plans. 

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"I want to make sure people don't forget, and that we do talk about in America what happened 20 years ago," he said. 

Speaking to the idea of someone possibly forgetting what happened on Sept. 11, 2001, Ret. FDNY Battalion Commander John V. LaBarbera told Fox News, "We will never let it happen."

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LaBarbera, who now serves on the foundation’s executive board, said despite how big the foundation has grown, "it's the small donations that have gotten us to where we are today."

"We need help. Whether it's a dollar, $11 a month, or your time, we could get it done with help from people that are all around this country, and they have been responding," LaBarbera said. 

Of the victims, he said: "There is (sic) times when we do think and cry and pray for their souls. But they're also up there shining down upon us, knowing the job that we're doing."