9/11 ceremony live updates: Families to gather at WTC, Pentagon, Shanksville to mark 25 years

On the morning of Sept. 11, 2001, 34-year-old New York City firefighter Stephen Siller had just finished his overnight shift when he heard a call come in on the scanner.

He parked his car by the Brooklyn Battery Tunnel, Siller Jr. said, put about 60 pounds of gear on his back, and ran through the tunnel to the South Tower of the World Trade Center.

Stephen Siller was among 343 New York City Fire Department members killed on 9/11. He was survived by his close-knit siblings, his wife Sally, and his five children, including Stephen Jr., who was 9 months old.

Siller Jr., now 25, doesn't have his own memories of his father, but he's poured his energy into honoring those who died on 9/11. And to commemorate the 25th anniversary of the terror attacks, he spent the last four months bringing a 16,900-pound steel beam from the World Trade Center to dozens of cities across the U.S. in hopes that seeing a piece of history up close will help Americans remember, learn and be inspired.

Twenty-five years after escaping the World Trade Center just minutes before the towers collapsed, Mike Dempsey, who now lives in North Carolina, is working to educate future generations about the September 11 attacks and support those affected by them.

Dempsey worked for Credit Suisse in World Trade Center 5, which was connected to the North Tower. His wife, Amy, worked on the 100th floor of the North Tower.

Twenty-five years after escaping the World Trade Center just minutes before the towers collapsed, Mike Dempsey is working to educate future generations about the September 11 attacks and support those affected by them.

In the years since the attacks, Dempsey has focused on education and helping others. He helped start the September 11th Education Trust and has worked with various charities supporting survivors, victims' families and first responders.

"We want the future generations to know what happened that day from people like myself and family members and first responders," Dempsey said.