A hijacked commercial plane approaches the World Trade Center shortly before crashing into the landmark skyscraper on September 11, 2001 in New York. Pic/AFP

A hijacked commercial plane approaches the World Trade Center shortly before crashing into the landmark skyscraper on September 11, 2001 in New York. Pic/AFP

A man with a fire extinguisher walks through rubble after the collapse of the first World Trade Center Tower on September 11, 2001, in New York. The man was shouting as he walked looking for victims who needed assistance. Both towers collapsed after being hit by hijacked passengers planes. Pic/AFP

A man with a fire extinguisher walks through rubble after the collapse of the first World Trade Center Tower on September 11, 2001, in New York. The man was shouting as he walked looking for victims who needed assistance. Both towers collapsed after being hit by hijacked passengers planes. Pic/AFP

US President George W. Bush has his early morning school reading event interrupted by his Chief of Staff Andrew Card (L) shortly after news of the New York City airplane crashes was available in Sarasota, Florida. Pic/AFP

US President George W. Bush has his early morning school reading event interrupted by his Chief of Staff Andrew Card (L) shortly after news of the New York City airplane crashes was available in Sarasota, Florida. Pic/AFP

A fiery blasts rocks the World Trade Center after it was hit by two airplanes on September 11, 2001 in New York City. This is frame 5 out of a sequence of 6. Peter C. Brandt/Getty Images/AFP

A fiery blasts rocks the World Trade Center after it was hit by two airplanes on September 11, 2001 in New York City. This is frame 5 out of a sequence of 6. Peter C. Brandt/Getty Images/AFP

This September 11, 2001 file photo shows Marcy Borders covered in dust as she takes refuge in an office building after one of the World Trade Center towers collapsed in New York. Borders was caught outside on the street as the cloud of smoke and dust enveloped the area. The bank worker who survived World Trade Center terror attack died at 42 after year-long battle with cancer on August 24, 2015. Pic/AFP

This September 11, 2001 file photo shows Marcy Borders covered in dust as she takes refuge in an office building after one of the World Trade Center towers collapsed in New York. Borders was caught outside on the street as the cloud of smoke and dust enveloped the area. The bank worker who survived World Trade Center terror attack died at 42 after year-long battle with cancer on August 24, 2015. Pic/AFP

An ambulance, covered with debris, is on fire after the collapse of the first World Trade Center Tower, September 11, 2001 in New York. Two hijacked passenger planes were crashed against the twin towers causing the collapsed of both buildings. Pic/AFP

An ambulance, covered with debris, is on fire after the collapse of the first World Trade Center Tower, September 11, 2001 in New York. Two hijacked passenger planes were crashed against the twin towers causing the collapsed of both buildings. Pic/AFP

Pedestrians run from the scene as one of the World Trade Center Towers collapses on September 11, 2001, in New York following a terrorist plane crash on the twin towers. The all-out war on terrorism unleashed by Washington after the attacks marked a turning point in US-Arab relations and nowhere more so than in once top ally Saudi Arabia. With 15 of the 19 suicide hijackers carrying Saudi nationality and mastermind Osama bin Laden being the scion of a leading Saudi family, the desert kingdom and world oil kingpin, suddenly found itself on the frontline of the war on terror prosecuted by US President George W. Bush. Pic/AFP

Pedestrians run from the scene as one of the World Trade Center Towers collapses on September 11, 2001, in New York following a terrorist plane crash on the twin towers. The all-out war on terrorism unleashed by Washington after the attacks marked a turning point in US-Arab relations and nowhere more so than in once top ally Saudi Arabia. With 15 of the 19 suicide hijackers carrying Saudi nationality and mastermind Osama bin Laden being the scion of a leading Saudi family, the desert kingdom and world oil kingpin, suddenly found itself on the frontline of the war on terror prosecuted by US President George W. Bush. Pic/AFP

Emergency personnel battle a fire at the Pentagon in Washington, DC, 11 September, 2001 after an airplane crashed into it. At the same time, two passenger planes were crashed into the twin towers of the World Trade Center in new York City. Both towers collapsed. Pic/AFP

Emergency personnel battle a fire at the Pentagon in Washington, DC, 11 September, 2001 after an airplane crashed into it. At the same time, two passenger planes were crashed into the twin towers of the World Trade Center in new York City. Both towers collapsed. Pic/AFP

An office filled with dust and damage has a view of the wreckage of the World Trade Center on September 25, 2001 in New York. Search and rescue efforts continue in the aftermath of the 11 September terrorist attack. Pic/AFP

An office filled with dust and damage has a view of the wreckage of the World Trade Center on September 25, 2001 in New York. Search and rescue efforts continue in the aftermath of the 11 September terrorist attack. Pic/AFP

This photo released by the New York City Office of Emergency Management on September 17, 2001, shows an aerial view of the World Trade Center on September 16, 2001. The twin towers of the center were destroyed by terrorists crashing commercial jet planes into the structures. Pic/AFP

This photo released by the New York City Office of Emergency Management on September 17, 2001, shows an aerial view of the World Trade Center on September 16, 2001. The twin towers of the center were destroyed by terrorists crashing commercial jet planes into the structures. Pic/AFP

A firefighter breaks down after the World Trade Center buildings collapsed on September 11, 2001 after two hijacked airplanes slammed into the twin towers in a terrorist attack. Mario Tama/Getty Images/AFP

A firefighter breaks down after the World Trade Center buildings collapsed on September 11, 2001 after two hijacked airplanes slammed into the twin towers in a terrorist attack. Mario Tama/Getty Images/AFP

An unidentified firefighter wipes a tear while saluting the casket of New York Fire Department Chaplin Reverend Mychal Judge on September 15, 2001, a victim of the World Trade Center attack in New York. Judge was killed while giving last rites at the scene of the attack. Pic/AFP

An unidentified firefighter wipes a tear while saluting the casket of New York Fire Department Chaplin Reverend Mychal Judge on September 15, 2001, a victim of the World Trade Center attack in New York. Judge was killed while giving last rites at the scene of the attack. Pic/AFP

Smoke and ash from the destroyed World Trade Center rises over the southern end of New York City's Manhattan behind the Statue of Liberty as seen from Jersey City, New Jersey on September 12, 2001. Terrorists hijacked two commercial airliners and crashed them into each of the towers of the Trade Center. Pic/AFP

Smoke and ash from the destroyed World Trade Center rises over the southern end of New York City's Manhattan behind the Statue of Liberty as seen from Jersey City, New Jersey on September 12, 2001. Terrorists hijacked two commercial airliners and crashed them into each of the towers of the Trade Center. Pic/AFP

This US Coast Guard handout photo received on September 9, shows a test of the Tribute in Light Memorial as it illuminates a passing cloud above lower Manhattan, just before the third anniversary of the attacks of September 11. Pic/AFP

This US Coast Guard handout photo received on September 9, shows a test of the Tribute in Light Memorial as it illuminates a passing cloud above lower Manhattan, just before the third anniversary of the attacks of September 11. Pic/AFP