Joe Caristo of Miami, who once worked at the World Trade Center, stands silently Sunday, Sept. 11, during a ceremony in New York marking the 10th anniversary of the 9/11 attacks on the World Trade Center. Caristo says he lost friends in the 2001 attacks on the twin towers.
Cho Sok Wells, accompanied by his wife Cathy, kisses their 10-month-old son Cristian while visiting his sister's memorial bench after the 10th anniversary 9/11 ceremony at the Pentagon in Arlington, Va., on Sunday.
Visitors embrace in front of the Wall of Names near the crash site of Flight 93 in Shanksville, Pa., on Sunday.
U.S. flight medic Sfc David Bibb of Santa Fe, N.M., holds an American flag on top of a helicopter Sunday to commemorate the 10th anniversary of the 9/11 attacks at Forward Operating Base Edi in Afghanistan's Helmand province.
People gather during a ceremony marking the 10th anniversary of the attacks on the World Trade Center Sunday, Sept. 11, 2011, outside the World Trade Center site in New York.
A young man holds his head as he sits in front of a memorial for FDNY firefighters from Ladder Company 20 who died at the World Trade Center on 9/1. New York City firefighters are commemorating the 10th anniversary of the 9/11 terrorist attacks and honoring the 343 firefighters who died in the line of duty.
Las Vegas firefighter Capt. Eric Littmann walks in a parade commemorating the 2001 attacks on the World Trade Center and the Pentagon, Sept. 11, 2011, in Las Vegas, Nev.
People observe a moment of silence during ceremonies at the World Trade Center site for the 10th anniversary of the terrorist attacks on lower Manhattan on September 11, 2001 in New York City.
Christoffer Molsins, a soldier from Denmark who is being deployed to Afghanistan, holds his dog tags while standing with thousands of others on Church Street in lower Manhattan as they listen to the ceremony marking the 10th anniversary of the 9/11 attacks on the World Trade Center in New York, Sept. 11, 2011.
Capt. Erik Schutz, 26, of Medina, Minn., right, and Capt. Matt Schachman, 28, of Wilmette, Ill., raise a new American flag to commemorate the tenth anniversary of the 9/11 attacks as Capt. Ron Hopkins, 27, left, of Honolulu, Hawaii, looks on Sept. 11, 2011 at Forward Operating Base Bostick in Kunar province, Afghanistan.
Helen Jordan of London reads ribbons of remembrance on a fence at St. Pauls Church in Lower Manhattan during events marking the 10th anniversary of the 9/11 attacks on the World Trade Center in New York, Sept. 11, 2011.
Fire fighters and other first responders receive applause as they wind their way through the seats at Parkview Field baseball stadium in Fort Wayne, Ind., Sept 11, 2011. The 9/11 Stair Climb memorial walk started at 8:46 a.m., the time the first plane hit the north tower of the World Trade Center. About 400 people attended the event.
Mourners embrace during tenth anniversary ceremonies at the site of the World Trade Center in New York, Sept. 11, 2011.
People react during ceremonies marking the 10th anniversary of the 9/11 attacks on the World Trade Center, in New York, Sept. 11, 2011.
Robert Peraza, who lost his son Robert David Peraza in the attacks at the World Trade Center, pauses on Sunday, Sept. 11, at his son's name at the North Pool of the 9/11 Memorial before the 10th anniversary ceremony.
Family members arrive Sunday at the check-in area before the ceremonies marking the 10th anniversary of the 9/11 attacks on the World Trade Center in New York.
President Barack Obama, right; first lady Michelle Obama; former President George W. Bush; and former first lady Laura Bush look out at the North Pool of the 9/11 memorial.
New York City police and firefighters and Port Authority police officers salute during the singing of the "Star Spangled Banner" at the Sept. 11 memorial, during the 10th anniversary ceremonies at the site on Sunday.
A man walks among nearly 3,000 flags set up as part of a remembrance in St. Louis, Mo., on the 10th anniversary of the Sept. 11 terrorist attacks.
People arrive Sunday for the ceremony marking the 10th anniversary of the Sept. 11 terrorist attacks on the World Trade Center.
Three small stones are placed over a name on one of the plaques in the '9/11 Memorial' outside Jerusalem on Sept. 11, 2011, during a 10th anniversary memorial ceremony marking the 9/11 terror attacks in the United States, which killed nearly 3,000 people, including five Israelis. It is customary at Jewish cemeteries to place stones on the graves of loved ones. The memorial here contains a large American flag made of bronze that appears to be billowing in the wind, and has plaques containing all of the nearly 3,000 names of the victims, the only site to do so outside the one at the World Trade Center in New York City.
Peace activists release white doves during a commemoration of the 10th anniversary of the 9-11 terror attacks in Berlin, Germany, on September 11, 2011.
Members of Clerkenwell Fire Station's Green Watch observe a minute of silence in London, England, on Sunday, remembering their fellow firefighters who lost their lives in the 9/11 terrorist attacks in New York.
High school students pose for a photo by a damaged replica of the Statue of Liberty in Ishinomaki, Japan, Sunday. As the world commemorated the 10th anniversary of the World Trade Center attacks, Sunday was doubly significant for Japan. It marked six months since the massive earthquake and tsunami on March 11.
The Tribute in Light shines above lower Manhattan, the Statue of Libertyand One World Trade Center, left, on Saturday.
Family and friends of those aboard Flight 93 gather on Saturday, Sept. 10, 2011, at the boulder that marks the crash site outside Shanksville, Pa. They were there the day before the 10th anniversary of the terrorist attacks after the dedication of the first phase of the permanent Flight 93 National Memorial.
Vice President Joe Biden speaks during the dedication of the Flight 93 memorial in Shanksville, Pa.. A long white stone wall bearing the names of those who struggled with al-Qaida terrorists on the fourth airliner to be hijacked on Sept. 11, 2001, was unveiled on the rural Pennsylvania field where the Boeing 757 crashed.
Former Presidents George W. Bush and Bill Clinton and former first lady Laura Bush bow their heads during ceremonies in Shanksville, Pa.
A family member of one of the victims of the crash of United Flight 93 walks along a part of the Flight 93 National Memorial following its dedication. The names of the 40 victims of the crash are inscribed on the marble panels.
People look out at the World Trade Center site on Sept. 10 in New York City.
Workers take off their hard hats off during the playing of the National Anthem after unfurling a flag on One World Trade Center overlooking the national Sept. 11 memorial on Sept. 10.
Workers scrub a waterfall pool at the National September 11 Memorial on Sept. 10 in New York.
A tribute to Sept. 11 is seen at Bryant Park on Sept. 10 in New York. There are 2,753 empty chairs -- one for each life lost in New York during the Sept. 11, 2001 attacks.
Flags are carried into St. Patrick's Cathedral in New York during a ceremony Sept. 10 to honor New York firefighters killed in the attacks.
A New York firefighter listens as the daughter of a firefighter who died on Sept. 11, 2001, speaks during the first repsponders' memorial service at St. Patrick's Cathedral in New York.
A visitor takes pictures of flags erected at Battery Park in Manhattan, on Sept. 10 as a part of a project called "One Flag One Life" to marking the 10th anniversary of the attacks.
The Score family hugs after participating in the "Hand In Hand, Remembering 9/11" event in Battery Park in New York Sept. 10.
A woman writes a message on the wall of remembrance memorial near the World Trade Center in New York on Sept. 10.
In Liberty State Park in Jersey City, N.J., on Sept. 10, a man looks at names on the wall of the newly opened Empty Sky memorial to victims of the 9/11 attacks on the World Trade Center. The memorial consists of two 30-foot-tall concrete and steel structures, inscribed with the names of the 746 people from New Jersey who died in the attacks.
Dr. Madeline Borquist of Carmel Valley, Calif., uses charcoal to outline the name of her niece, Alison Marie Wildman, during the memorial dedication of the Empty Sky memorial at Liberty State Park on Sept. 10 in Jersey City, N.J. Wildman was killed in the terrorist attacks.
Angela Calos, left, and Heather Benedetto visit the National 9/11 Pentagon Memorial on Sept. 10 in Washington. The memorial commemorates the 184 people who died at the Pentagon and on American Airlines Flight 77.
President Barack Obama hugs a visitor during a visit to Arlington National Cemetery in Washington on Sept. 10.
Judy and Bob Poore place a flag at Kennesaw Mountain National Battlefield Park in Georgia on Sept. 10 to help commemorate the 10th anniversary and remember their friend Ann Ransom, one of nearly 3,000 people who died in the attacks. A flag was placed on the battlefield for each victim; the flags will remain flying through Sept. 16.