The nation pauses Thursday to mark the thirteenth anniversary of the Sept. 11, 2001, terror attack.
Sept 11 Anniversary A firefighter looks at a memorial mural on the outside of firehouse Engine 10 Company 10 adjacent to the World Trade Center in New York, Thursday, Sept. 11, 2014. Three hundred forty three New York firefighters were killed in the terrorist attacks of Sept. 11, 2001. (AP Photo/Mark Lennihan)
AP Photo/Mark Lennihan
Sept 11 Anniversary Jose Colon, of New York, looks up at 1 World Trade Center before a ceremony marking the 13th anniversary of the Sept. 11, 2001 attacks, Thursday, Sept. 11, 2014, in New York. (AP Photo/Jason DeCrow)
AP Photo/Jason DeCrow
Sept 11 Anniversary A police K-9 unit stands a few blocks from the National September 11 Memorial at the World Trade Center site before a ceremony marking the 13th anniversary of the Sept. 11, 2001 attacks, Thursday, Sept. 11, 2014, in New York. (AP Photo/Jason DeCrow)
AP Photo/Jason DeCrow
Sept 11 Anniversary United States Navy veteran Richard Fill, of Easton, Penn., looks up at 1 World Trade Center during a moment of silence on the 13th anniversary of the Sept. 11, 2001 attacks, Thursday, Sept. 11, 2014, in New York. (AP Photo/Jason DeCrow)
AP Photo/Jason DeCrow
Obama Sept 11 A Marine bugler plays Taps as President Barack Obama, first lady Michelle Obama, Vice President Joe Biden, and others, stand on the South Lawn of the White House in Washington, Thursday, Sept. 11, 2014, as they mark the 13th anniversary of the 9/11 attacks. (AP Photo/Charles Dharapak)
AP Photo/Charles Dharapak
Sept 11 Anniversary A police counterterrorism officer stands a few blocks from the National September 11 Memorial at the World Trade Center site before a ceremony marking the 13th anniversary of the Sept. 11, 2001 attacks, Thursday, Sept. 11, 2014, in New York. (AP Photo/Jason DeCrow)
AP Photo/Jason DeCrow
Sept 11 Obama Flowers sit on one of the benches of the Pentagon Memorial at the at the Pentagon, Thursday, Sept. 11, 2014. President Barack Obama will attend the wreath laying later this morning to to mark the 13th anniversary of the 9/11 attacks. (AP Photo/Pablo Martinez Monsivais)
AP Photo/Pablo Martinez Monsivais
Sept 11 Anniversary A woman walks with a child near United States flags with 1 World Trade Center, rear left, in the background, Thursday, Sept. 11, 2014, in Jersey City, N.J. The country is observing the 13th anniversary of the Sept. 11, 2001 terrorist attacks on the World Trade Center. (AP Photo/Julio Cortez)
AP Photo/Julio Cortez
Sept 11 Obama A woman reaches out to touch rose on one of the benches of the Pentagon Memorial at the at the Pentagon, Thursday, Sept. 11, 2014. President Barack Obama will attend the wreath laying later this morning to to mark the 13th anniversary of the 9/11 attacks. (AP Photo/Pablo Martinez Monsivais)
AP Photo/Pablo Martinez Monsivais
Barack Obama, Michelle Obama, Joe Biden President Barack Obama, first lady Michelle Obama, Vice President Joe Biden, and others, put their hands on their hearts during the playing of Taps on the South Lawn of the White House in Washington, Thursday, Sept. 11, 2014, as they mark the 13th anniversary of the 9/11 attacks. (AP Photo/Charles Dharapak)
AP Photo/Charles Dharapak
Barack Obama, Michelle Obama, Joe Biden President Barack Obama, first lady Michelle Obama, Vice President Joe Biden, and others, stand on the South Lawn of the White House in Washington, Thursday, Sept. 11, 2014, as they observe a moment of silence to mark the 13th anniversary of the 9/11 attacks. (AP Photo/Charles Dharapak)
Obama Sept 11 A man places a flower on one of the benches of the Pentagon Memorial at the at the Pentagon, Thursday, Sept. 11, 2014. President Barack Obama will attend the wreath laying later this morning to to mark the 13th anniversary of the 9/11 attacks. (AP Photo/Pablo Martinez Monsivais)
AP Photo/Pablo Martinez Monsivais
Sam Pulia Sam Pulia, mayor of Westchester, Ill., and a former police officer of the same town, mourns over the name of his cousin, New York firefighter Thomas Anthony Casoria, who was killed in the South Tower in the attacks of Sept. 11, 2001, prior to the the memorial observances held at the site of the World Trade Center in New York, Thursday, Sept. 11, 2014. This year marks the 13th anniversary of the terrorist attacks that killed nearly 3,000 people at the World Trade Center, Pentagon and on Flight 93 over Pennsylvania. (AP Photo/Andrew Burton, Pool)
AP Photo/Andrew Burton, Pool
White roses are placed in an inscribed name along the edge of the North Pool during memorial observances on the 13th anniversary of the Sept. 11 terror attacks on the World Trade Center in New York, Thursday, Sept. 11, 2014. In New York, family members of those killed at the World Trade Center will read the names of the victims at a ceremony at ground zero. (AP Photo/Justin Lane, Pool)
AP Photo/Justin Lane, Pool
CORRECTION Sept 11 Anniversary Flowers are placed at the South Tower Memorial Pool before memorial observances held at the site of the World Trade Center in New York, Thursday, Sept. 11, 2014. (AP Photo/The New York Times, Chang W. Lee, Pool)
AP Photo/The New York Times, Chang W. Lee, Pool
Sept 11 Anniversary Police officers stand watch outside the World Trade Center, Thursday, Sept. 11, 2014 in New York. Three hundred forty three New York firefighters were killed in the terrorist attacks of Sept. 11, 2001. Behind them are the transportation hub, center, and 1 World Trade Center, top. (AP Photo/Mark Lennihan)
AP Photo/Mark Lennihan
Sept 11 Anniversary A firefighter with Engine 10 Company 10 puts on his gear as a call comes into his firehouse adjacent to the World Trade Center, Thursday, Sept. 11, 2014 in New York. Three hundred forty three New York firefighters were killed in the terrorist attacks of Sept. 11, 2001. (AP Photo/Mark Lennihan)
AP Photo/Mark Lennihan
New York Commemorates 13th Anniversary Of September 11th Attacks A wilting rose is left in remembrance of those lost before the memorial observances held at the site of the World Trade Center in New York, Sept. 11, 2014. This year marks the 13th anniversary of the September 11th terrorist attacks that killed nearly 3,000 people at the World Trade Center, Pentagon and on Flight 93. (AP Photo/POOL, Andrew Burton)
AP Photo/POOL, Andrew Burton
Sept 11 Anniversary Port Authority Police Officer Donna Przybyszewski takes a moment to herself before family members are let in for the memorial observances held at the site of the World Trade Center in New York, Sept. 11, 2014. This year marks the 13th anniversary of the September 11th terrorist attacks that killed nearly 3,000 people at the World Trade Center, Pentagon and on Flight 93. (AP Photo/POOL, Andrew Burton)
AP Photo/POOL, Andrew Burton
New York Commemorates 13th Anniversary Of September 11th Attacks Port Authority Police Officer Donna Przybyszewski takes a moment to herself before family members are let in for the memorial observances held at the site of the World Trade Center in New York, Sept. 11, 2014. This year marks the 13th anniversary of the September 11th terrorist attacks that killed nearly 3,000 people at the World Trade Center, Pentagon and on Flight 93. (AP Photo/POOL, Andrew Burton)
AP Photo/POOL, Andrew Burton
APTOPIX Sept 11 Pennsylvania Rick Sarmiento, center, embraces Karen Bingham, left, and Nancy Root, right, during a visit to the Flight 93 National Memorial on Wednesday, Sept. 10, 2014, Shanksville, Pa. Karen Bingham's son Mark Bingham was a passenger on Flight 93, as was Nancy Root's cousin Lorraine G. Bay. The memorial marks the spot where United Airlines Flight 93 crashed 13 years ago in a reclaimed strip mine some 75 miles southeast of Pittsburgh after passengers fought back against hijackers. (AP Photo/Gene J. Puskar)
AP Photo/Gene J. Puskar
Sept 11 Pennsylvania Forty luminarias in memory of the 40 passengers and crew of Flight 93 sit in front of the Wall of Names at the Flight 93 National Memorial in Shanksville, Pa., on Wednesday, September 10, 2014. (AP Photo/Gene J. Puskar)
AP Photo/Gene J. Puskar
ADDITION Sept 11 Pennsylvania Visitors to the Flight 93 National Memorial hold a giant flag as they participate in a sunset memorial service at sunset on Wednesday, Sept. 10, 2014, in Shanksville, Pa. (AP Photo/Gene J. Puskar)
AP Photo/Gene J. Puskar
Sept 11 Pennsylvania A flag is placed at the base of the Wall of Names that contains the names of the 40 passengers and crew of Flight 93 at the Flight 93 National Memorial on Wednesday, Sept. 10, 2014, in Shanksville, Pa. (AP Photo/Gene J. Puskar)
AP Photo/Gene J. Puskar
Sept 11 Anniversary A man visits a memorial set up to honor the victims of the Sept. 11, 2001 attacks, on the campus of Pepperdine University on Wednesday, Sept. 10, 2014, in Malibu, Calif. (AP Photo/Jae C. Hong)
AP Photo/Jae C. Hong
Sept 11 Anniversary The Tribute in Light rises behind buildings adjacent to the World Trade Center complex at the National September 11 Memorial, Monday, Sept. 8, 2014, in New York. The tribute, an art installation of 88 searchlights aiming skyward in two columns, is a remembrance of the Sept. 11, 2001, attacks. (AP Photo/Charles Sykes)
AP Photo/Charles Sykes
Steven Spaltro Steven Spaltro, of Middletown, N.J., stands with his dog Tyson in front of the Empty Sky Memorial at Liberty State Park, Thursday, Sept. 11, 2014, in Jersey City, N.J. The country is observing the 13th anniversary of the terrorist attacks on the World Trade Center. (AP Photo/Julio Cortez)
AP Photo/Julio Cortez
APTPOIX Sept 11 Anniversary The moon appears between the beams from the Tribute in Light memorial honoring the victims of the Sept. 11 terrorist attacks as 1 World Trade Center, left, stands on the 13th anniversary, Thursday, Sept. 11, 2014, in Jersey City, N.J. The tribute is an art installation of 88 searchlights aiming skyward in two columns. (AP Photo/Julio Cortez)
AP Photo/Julio Cortez
Sept 11 Anniversary Pennsylvania Family and friends of the 40 passengers and crew of Flight 93 walk down the path that follows the flight path of Flight 93 after visiting a boulder, top rear center, that marks the crash site of Flight 93 at the Flight 93 National Memorial in Shanksville, Pa. after a Service of Remembrance Thursday, Sept. 11, 2014, the 13th anniversary of the Sept. 11 attacks. (AP Photo/Gene J. Puskar)
AP Photo/Gene J. Puskar
Sept 11 Anniversary Pennsylvania Visitors to the Flight 93 National Memorial in Shanksville, Pa.. listen as the names of the 40 passengers and crew of Flight 93 are read during a Service of Remembrance at the Flight 93 National Memorial in Shanksville, Pa., Thursday, Sept. 11, 2014 as the nation marks the 13th anniversary of the Sept. 11 attacks. (AP Photo/Gene J. Puskar)
AP Photo/Gene J. Puskar
Afghanistan U.S. service members salute during a ceremony on the thirteenth anniversary of the 9/11 terrorist attacks in front of the World Trade Center Memorial at Bagram Airfield, Afghanistan Thursday, Sept. 11, 2014. (AP Photo/Massoud Hossaini)
AP Photo/Massoud Hossaini
Afghanistan U.S. service members stand during a ceremony on the thirteenth anniversary of the 9/11 terrorist attacks in front of the World Trade Center Memorial, at Bagram Airfield, Afghanistan Thursday, Sept. 11, 2014. (AP Photo/Massoud Hossaini)
AP Photo/Massoud Hossaini
Afghanistan U.S. service members stand guard as they carry the U.S. flag and a unit flag during a ceremony on the thirteenth anniversary of the 9/11 terrorist attacks in front of the World Trade Center Memorial at Bagram Airfield, Afghanistan Thursday, Sept. 11, 2014. (AP Photo/Massoud Hossaini)
AP Photo/Massoud Hossaini
Sept 11 Anniversary NY Dennis Riga, of New Rochelle, N.Y., kneels in remembrance on the 13th anniversary of the Sept. 11 attacks, Thursday, Sept. 11, 2014, in New York. (AP Photo/Jason DeCrow)
AP Photo/Jason DeCrow
Jorge Maldonado, Lisa Maldonado, 9/11 Memorial. Jorge, left, and Lisa Maldonado, of New York City, hug as they reflect at a 9/11 Fallen Heroes Memorial after it was unveiled outside the Hillsborough County Sheriff's Office, Thursday, Sept. 11, 2014, in Tampa, Fla. The memorial includes a beam from the World Trade Center Tower 2. People across the country are remembering on the 13th anniversary of the 2001 terrorist attacks. (AP Photo/Chris O'Meara)
AP Photo/Chris O'Meara
Barack Obama, Chuck Hagel President Barack Obama and Defense Secretary Chuck Hagel stand during a ceremony the Pentagon, Thursday, Sept. 11, 2014, to mark the 13th anniversary of the 9/11 attacks. (AP Photo/Charles Dharapak)
AP Photo/Charles Dharapak
Barack Obama, Larnell Maurice Perry President Barack Obama picks up 13-month-old Larnell Maurice Perry Jr., grandson of Angelene C. Carter, who was killed in the September 11 attacks at the Pentagon, at the Pentagon, Thursday, Sept. 11, 2014, during a ceremony where Obama marked the 13th anniversary of the 9/11 attacks. (AP Photo/Charles Dharapak)
AP Photo/Charles Dharapak
Wayne Russo, Lito Deleon Lito Deleon holds a photo of friend Wayne Russo, who died in the Sept 11, 2001 attacks, during memorial observances held at the site of the World Trade Center in New York, Thursday, Sept. 11, 2014. The two played together in the punk rock band "Stetz" in Union, N.J. in the 1980's. Family and friends of those who died read the names of the nearly 3,000 people killed in New York, at the Pentagon and near Shanksville, Pennsylvania. (AP Photo/Mark Lennihan, Pool)
AP Photo/Mark Lennihan, Pool
Sept 11 Anniversary Former New York Mayors Rudy Giuliani, left, and Michael Bloomberg, center, talk with New Jersey Gov. Chris Christie during memorial observances held at the site of the World Trade Center in New York, Thursday, Sept. 11, 2014. Standing behind them is New York Mayor Bill de Blasio. Family and friends of those who died read the names of the nearly 3,000 people killed in New York, at the Pentagon and near Shanksville, Pennsylvania. (AP Photo/Mark Lennihan/Pool)
AP Photo/Mark Lennihan/Pool
1 World Trade Center
Port Authority Police Assistant Chief Norma Hardy rings the bell signifying the collapse of the first tower during memorial observances on the 13th anniversary of the Sept. 11 terror attacks on the World Trade Center in New York, Thursday, Sept. 11, 2014. Family and friends of those who died read the names of the nearly 3,000 people killed in New York, at the Pentagon and near Shanksville, Pennsylvania. (AP Photo/The Record of Bergen County, Chris Pedota, Pool)
AP Photo/The Record of Bergen County, Chris Pedota, Pool
Barack Obama President Barack Obama bows his head during a moment of silence at the Pentagon, Thursday, Sept. 11, 2014, during a ceremony to mark the 13th anniversary of the 9/11 attacks. (AP Photo/Pablo Martinez Monsivais)
AP Photo/Pablo Martinez Monsivais
Barack Obama President Barack Obama pauses after laying a wreath at the Pentagon, Thursday, Sept. 11, 2014, to mark the 13th anniversary of the 9/11 attacks. (AP Photo/Charles Dharapak)
AP Photo/Charles Dharapak
Sept 11 Anniversary Members of the New York Police Department, Fire Department of New York and Port Authority of New York and New Jersey Police Department carry an American flag at the beginning of the memorial observances on the 13th anniversary of the Sept. 11 terror attacks on the World Trade Center in New York, Thursday, Sept. 11, 2014. In New York, family members of those killed at the World Trade Center will read the names of the victims at a ceremony at ground zero. (AP Photo/Andrew Burton, Pool)
AP Photo/Andrew Burton, Pool
Capitol Sept. 11 As the American flag waves at half-staff on the anniversary of the 2001 terror attacks, workmen pause amid the scaffolding during repair work on the dome of the Capitol in Washington, Thursday, Sept. 11, 2014. (AP Photo/J. Scott Applewhite)
AP Photo/J. Scott Applewhite
Sept 11 Anniversary A memorial for firefighter Gerald T. Atwood is attached to an American flag in a sea of American flags during a memorial in Matthews, N.C., on the 13th anniversary of the Sept. 11, 2001 attacks, Thursday, Sept. 11, 2014. The 2,997 American flags are displayed for each person lost in the attacks. (AP Photo/Chuck Burton)
AP Photo/Chuck Burton
Barack Obama, Chuck Hagel, Martin Dempsey From left, President Barack Obama, Defense Secretary Chuck Hagel, and Joint Chiefs Chairman Gen. Martin Dempsey, participate in a ceremony at the Pentagon, Thursday, Sept. 11, 2014, to mark the 13th anniversary of the 9/11 attacks. (AP Photo/Pablo Martinez Monsivais)
AP Photo/Pablo Martinez Monsivais
13th anniversary of 9/11 terror attacks Paola Braut, of Belgium, kisses a photograph of her son Patrice along the edge of the North Pool during memorial observances on the 13th anniversary of the Sept. 11 terror attacks on the World Trade Center in New York, Thursday, Sept. 11, 2014. In New York, family members of those killed at the World Trade Center will read the names of the victims at a ceremony at ground zero. (AP Photo/Justin Lane, Pool)
AP Photo/Justin Lane, Pool
Sophia Demos, Eleni Tsokanis Sophia Demos carries her daughter Eleni Tsokanis, 1, as they walk past a sea of American flags during a memorial in Matthews, N.C., on the 13th anniversary of the Sept. 11, 2001 attacks, Thursday, Sept. 11, 2014. The 2,997 American flags are displayed for each person lost in the attacks. (AP Photo/Chuck Burton)
AP Photo/Chuck Burton
Sept 11 Anniversary Anthony DeBlase, left, and his mother Anita, right, hold the paper as Alexandra DeBlase rubs the name of their lost loved one James V DeBlase during memorial observances on the 13th anniversary of the Sept. 11 terror attacks on the World Trade Center in New York, Thursday, Sept. 11, 2014. In New York, family members of those killed at the World Trade Center will read the names of the victims at a ceremony at ground zero. (AP Photo/The Daily News, Robert Sabo, Pool)
AP Photo/The Daily News, Robert Sabo, Pool
An American flag is placed in an inscribed name along the edge of the North Pool during memorial observances on the 13th anniversary of the Sept. 11 terror attacks on the World Trade Center in New York, Thursday, Sept. 11, 2014. In New York, family members of those killed at the World Trade Center will read the names of the victims at a ceremony at ground zero. (AP Photo/Justin Lane, Pool)
AP Photo/Justin Lane, Pool
A woman pauses at the edge of the North Pool during memorial observances on the 13th anniversary of the Sept. 11 terror attacks on the World Trade Center in New York, Thursday, Sept. 11, 2014. In New York, family members of those killed at the World Trade Center will read the names of the victims at a ceremony at ground zero. (AP Photo/Justin Lane, Pool)