9/11 25th anniversary live updates: Families gather for ceremonies at World Trade Center, Pentagon, Shanksville

For the first time, the 9/11 Memorial & Museum added a seventh moment of silence at this year's ceremony to honor those who have died of illnesses related to their time at or near the World Trade Center site.

For the past 24 years, there have been six moments of silence: two to mark the times when the planes struck the World Trade Center towers; one to mark when a plane struck the Pentagon; one to mark when a plane crashed in Shanksville, Pennsylvania; and the two times the World Trade Center towers collapsed. Each moment of silence is followed by a bell toll.

This new, seventh moment of silence was observed at the conclusion of the reading of the names and will be a permanent part of the annual ceremony.

More than 9,000 people have now died from 9/11-related illnesses, approximately three times the number killed on Sept. 11, 2001, according to the World Trade Center Health Program.

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ABC News has gone inside the 9/11 Memorial & Museum to witness the hallowed space that's dedicated to making sure people never forget.

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Visit 9/11 Memorial & Museum in honor of 25th anniversary of Sept. 11, 2001A quarter-century after the September 11, 2001 terror attacks, ABC News goes inside the 9/11 Memorial & Museum to witness the hallowed space that's dedicated to making sure people never forget.

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Family members of 9/11 victims are continuing to read their names at the downtown Manhattan ceremony.

The granddaughter of FDNY Lt. Robert Wallace said, “Not many moments go by where I don’t think about you.”

“Papa, even though we never met, I see you in everything. In mom, in Nana … and your seven grandkids,” she said.

“We will never forget your heroic sacrifice,” she said.

Cantor Fitzgerald employee William Raub's daughter was just 6 years old on 9/11.

"I can still feel how much you love me 25 years later,” she said, “and I’m so lucky and so proud to be your daughter. We miss you so much."

The wife of Cantor Fitzgerald employee John Candela said, "Thank you, God, for putting John in my life and for the peace I have knowing that I will see John again in heaven."

“John, I love you tons. I miss your hugs. God bless us all and God bless America."

The names of all the victims can be seen here on the 9/11 Memorial & Museum website.

Hundreds of people gathered in Shanksville, Pennsylvania, to mark the 25th anniversary of United Flight 93's crash.

The family members of the 40 passengers and crew who were killed read their names, accompanied by bells.

The color guard folded a U.S. flag and placed it on a giant rock near the edge of a grove of hemlocks. That rock is where some of the very last pieces of Flight 93 came to rest.

-ABC News' Stephanie Ramos and Janice McDonald