New York, New York - The families of 9/11, beneath a blue sky reminiscent of a clear September morning 20 years ago, gathered once more Saturday to remember those killed in the terrorist attack that toppled the World Trade Center.

The relatives began arriving early at the hallowed lower Manhattan site to mark the two-decade anniversary of the deadliest terrorist attack ever on US soil, honoring the first responders and downtown workers who never came home on September 11, 2001 as two hijacked planes took down the twin towers and killed 2,753 victims.

"These 20 years felt like a long time, and a short time," said Mike Low, whose flight attendant daughter Sara was killed aboard one of the hijacked planes. "It felt like an evil specter had descended on our world, but it was also a time when many people acted above and beyond the ordinary."

President Joe Biden, who attended last year’s solemn service, returned for his first time as the nation’s commander in chief with first lady Jill Biden.

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One of the president’s childhood friends lost a son in the attack that also killed 343 members of the FDNY, 23 members of the NYPD members, and 37 members of the Port Authority Police.

The event began on the bright morning with an honor guard carrying a large American flag as they marched in silence through the crowd of mourners – followed by a performance of the National Anthem. Many family members clutched smaller flags, flowers and framed photos of the dead.

At 8:46 AM, a moment of silence was observed to mark the moment when the 110-story North Tower was struck by the first plane. It was followed by the reading of the victims’ names by family members, the emotional centerpiece of the annual memorial service, with tears and choked voices reflecting the lingering pain of the day’s death toll.

"You always carried the good torch, shining brightly wherever you went and (daughter) Alexa will carry it," said Patti Edwards, whose husband Dennis Michael Edwards died on the 105th floor in the Cantor Fitzgerald offices.

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"For as long as we live, people will know your name and honor your memory. We love you, Den."

Following a second moment of silence at 9:03 AM., when the second plane hit the South Tower, unannounced guest Bruce Springsteen appeared with his guitar and harmonica to perform his song I’ll See You in My Dreams.

"May God bless our fallen brothers and sisters, their families, their friends and their loved ones," said the New Jersey native. Broadway actor Kelli O’Hara also sang at the somber service.

The crowd included kids now grown into adults, raised by single parents in the aftermath of the carnage. Tears still flowed two decades later, the wounds fresh despite the passage of time, as the bell tolled twice more to mark the moments when each skyscraper toppled: The south tower at 9:59 AM, and the north tower 21 minutes later.

Joining Biden for the 20-year anniversary were former Presidents Barack Obama and Bill Clinton.

New York’s new governor, Kathy Hochul, made her first appearance at the event as the state’s chief executive.

Mexican immigrant Gustavo Campos (51), now a New Yorker, came with his son and his memories to attend the annual ceremony.

“It’s not only important to remember September 11 but September 12, the next day (when) we were united," said Campos. "At that time, there were no Republicans, no Democrats, rich, poor. All of us as a country were united in our grief of what had happened."

Ilia Rodriguez (78) visited with her daughter Olga Colon to mourn her paramedic son Carlos Rey Lilla, killed while helping people out of the South Tower.

"He was a beautiful guy, he was a beautiful son," said Rodriguez. "He was a friend, family ... He was trying to take people out, and give them aid to go to the hospital. After he went back in, nobody saw him after."

More than 1,100 victims of the trade center attack remain unidentified 20 years later, with the city Medical Examiner identifying the remains of two people just last week through DNA analysis.