The moments of the attacks were remembered by bells and silence, reported .
"That day we felt isolated, but not for long and not from each other," Mayor Michael Bloomberg said as the ceremony began. "Six years have passed, and our place is still by your side."
The dreary, gray skies created a grim backdrop, and a sharp contrast to the clear blue of that morning in 2001. This was the first time in six years that the anniversary has fallen on a Tuesday -- the day the attacks occurred in 2001 -- and the first time that it has rained.
Among the first family members down the ramp was Marjorie Miller, whose late husband Joel died in the trade center attacks. She said the rain was almost welcome after five consecutive years of Sept. 11 sunshine.
"A lot of tears coming down from up there," she said, gesturing toward the sky, "and a lot of tears down here."
Also for the first time, the ceremony was not at the trade center -- because of the construction that now fills the vast city block where the World Trade Center once stood.
An estimated 3,500 family members and mourners turned out, down from 4,700 attendees at the fifth anniversary.
Kathleen Mullen, whose niece Kathleen Casey died in the attacks, said the park across the street was close enough.
"Just so long as we continue to do something special every year, so you don't wake up and say, 'Oh, it's 9/11,' " she said.
Once again, the city paused to listen as the names of the 2,750 victims were read. The mourners were then allowed to walk into the construction pit and drop roses into a pool of water, which rippled from the raindrops and reflected the dark skies above. CBS Evening News anchor Katie Couric reports that this could be the family members' last descent into ground zero before the Freedom Tower and a 9/11 Memorial rise in its place.
The firefighters and first responders who helped rescue thousands that September day in 2001 and later recovered the dead, read the victims' names for the first time. Many of those rescuers are now ill with respiratory problems and cancers themselves, and they blame the illnesses on exposure to the fallen towers' toxic dust.
"We need to put our arms around the people that have actually both suffered injury and the families that were involved. I don't think this is a short-run affair," New Jersey Gov. Jon S. Corzine told WCBS-TV.
Also for the first time, the name of a victim who survived that towers' collapse but died five months later of lung disease blamed on the dust she inhaled was added to the official roll.
Felicia Dunn-Jones, an attorney, was working a block from the World Trade Center. She became the 2,974th victim linked to the four attack sites where hijacked airliners hit the two towers, the Pentagon and a field near Shanksville, Pa., where federal investigators say the passengers of United Airlines Flight 93 fought the hijackers on the rallying cry "Let's roll!"
Couric reports a solemn crowd gathered in a foggy field outside Shanksville, Pennsylvania Tuesday morning to honor the passengers and crew of the doomed Flight 93.
Governor Edward Rendell spoke to the mourners there, telling them that, "People who love freedom and democracy around the world never forget what the 40 brave men and women did protecting our country and protecting democracy."
"As American citizens we're all looking at our heroes," said Kay Roy, whose sister Colleen Fraser, died in that crash. "These are our heroes and I'm glad that one of my family members happens to be one of these heroes."
At the Pentagon, Gen. Peter Pace, chairman of the Joint Chiefs of Staff, spoke at the wall where one plane crashed and told the victims' families that their loved ones will be remembered, reports .
"I do not know the proper words to tell you what's in my heart, what is in our hearts, what your fellow citizens are thinking today. We certainly hope that somehow these observances will help lessen your pain," he said.
In a speech to family members of some of the Pentagon victims, Defense Secretary Robert Gates vowed that: "The enemies of America ... will never again rest easy, for we will hunt them down relentlessly and without reservation."
In New York, firefighters shared the stage with former Mayor Rudy Giuliani, who many victims' families and firefighters said should not speak because he is running for president. Giuliani has made his performance in the months after the 2001 terrorist attacks the cornerstone of his campaign, but he said his desire to be there Tuesday was entirely personal.
"It was a day with no answers, but with an unending line of people who came forward to help one another," he told those gathered at the memorial service.
After he descended to the trade center site, however, one man yelled "Scum! Scum!" at him, and a woman from the family line said Giuliani did not allow enough time for the search for victims' remains. "Because of Giuliani, we never had closure," said Sabrina Rivera. Giuliani left without speaking to reporters.
Sen. Hillary Rodham Clinton, seeking the Democratic Party presidential nomination, also attended the ceremonies. Republican Mitt Romney, another presidential contender, issued a statement describing the attacks as the day "radical Islamists brought terror to our shores."
Democratic candidate Barack Obama called for the country to "recapture the sense of common purpose," while saying the "threat to America has only grown." Fellow Democratic presidential hopeful Bill Richardson called on President Bush and Congress to strengthen intelligence gathering and pursue a foreign policy that will eradicate terrorism.
At the main U.S. base at Afghanistan, service members bowed their heads in memory of the victims.
But, the release of the bin Laden video Tuesday underscored the U.S.'s failure to find bin Laden despite Bush's vow in the wake of the attacks to take him "dead or alive".
The video featured an audiotape introduction by the al Qaeda leader and showed hijacker Waleed al-Shehri addressing the camera.
"We shall come at you from your front and back, your right and left," al-Shehri, one of the hijackers on American Airlines Flight 11, which hit the World Trade Center, warns Americans.
"It is true that this young man was little in years, but the faith in his heart was big," bin Laden said, paying his own tribute to the hijacker.
"Six years after the event, it's still dominating our lives, because it changed the whole tone and tenor of behavior," presidential historian Douglas Brinkley told CBS News.
"Anybody that's going to an airport or trying to get on a subway or just simply having to walk into a business building and flashes their ID are in a way victims of what happened during 9/11."
In all, 2,974 victims were killed by the Sept. 11 attacks: 2,750 at the World Trade Center, 40 in Pennsylvania and 184 at the Pentagon. Those numbers do not include the 19 hijackers.