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An injured woman is assisted out of the World Trade Center after a blast ripped through the world's second tallest office complex, killing six people and injuring more than 1,000 people in New York, in this February 26, 1993 file photograph. The Port Authority of New York and New Jersey will commemorate the 20th anniversary of the 1993 World Trade Center bombing on February 26, with a tribute to the six victims and an unborn child who lost their lives during the attack. REUTERS/Greta Pratt

People run from the underground PATH rail station after an explosion at the World Trade Center in New York Friday, Feb. 26, 1993. A terrorist bomb killed six people and injured more than 1,000. (AP Photo/Marty Lederhandler)

Passersby and workers rush from the World Trade Center in New York on Feb. 26, 1993 after an explosion rocked the landmark complex. The underground explosion was caused by a terrorist's bomb and killed six people and injured more than 1,000. (AP Photo/Marty Lederhandler)

FBI investigators make their way to the underground parking garage at the World Trade Center in New York, March 5, 1993, as they continue their investigation into last week's blast at the twin towers. Authorities have made an arrest in connection with the case. (AP Photo/Paul Hurschmann)

New York City police and firefighters inspect the bomb crater inside the World Trade Center on February 27, 1993, one day after the fatal attack by an Islamic faction. Six people were killed and more than 1,000 injured in the bombing. (AP Photo/Richard Drew)

A destroyed car lies underneath a section of rubble in the sub-basement of New York's World Trade Center, seen Feb. 28, 1993, after an explosion. Officials continue to investigate the cause and the extent of the damage at the twin towers. (AP Photo/Ron Frehm)

A New York City police officer leads a woman to safety following an underground explosion at the World Trade Center on Feb. 26, 1993. Hundreds were injured in the blast which caused the ceiling of a train station to collapse and set off fires below the twin towers. (AP Photo/Alex Brandon)

Victims of a fire at the World Trade Center in New York are treated at the scene after an explosion rocked the complex. A group of terrorists blew up explosives in an underground parking garage under one of the towers, killing six people and ushering in an era of terrorism on American soil. (AP Photo/Marty Lederhandler, File)

An injured man is aided by rescue workers after an explosion rocked the World Trade Center in New York, Feb. 26, 1993. (AP Photo/Joe Tabacca)

A man sits on the curb near the World Trade Center in New York after an explosion from an underground parking garage rocked the complex, Feb. 26, 1993. (AP Photo/Joe Tabacca)

Two New York City police officers help an injured women away from the scene of the World Trade Center explosion on February 26, 1993. A group of terrorists blew up explosives in an underground parking garage under one of the towers, killing six people and ushering in an era of terrorism on American soil. (AP Photo/Joe Tabacca, File)

A police officer surveys blast damage to a car in front of the World Trade Center after a blast ripped through the world's second tallest office complex, killing six people and injuring more than 1,000 people in New York on February 26, 1993. The Port Authority of New York and New Jersey will commemorate the 20th anniversary of the 1993 World Trade Center bombing on February 26, with a tribute to the six victims and an unborn child who lost their lives during the attack. REUTERS/Mike Segar

A clock, which reflects the time of the blast at the World Trade Center, sits in the wreckage of a vehicle at an impound lot in Brooklyn, March 9, 1993. (AP Photo/Kevin Larkin)

Firefighters in a cherry picker remove an explosion victim on a gurney outside one of the World Trade Center's twin towers in New York, after an explosion rocked the complex. (AP Photo/Alex Brandon, File)

Workers peer through broken windows of the World Trade Center in New York on Feb. 26, 1993, after an explosion in an underground garage rocked the twin towers complex. Heavy smoke, caused by underground fires, was reported throughout the buildings, causing the evacuation of the buildings. (AP Photo/Alex Brandon)

Helicopters jockey for a position over the World Trade Center in New York following a noontime blast, which rocked the twin towers complex on February 26, 1993. (AP Photo/Ron Frehm, File)

Manhattan's West Street is jammed with police and emergency service vehicles in the aftermath of yesterday's explosion that rocked New York's World Trade Center's twin towers and the Vista Hotel, foreground right, Feb. 27, 1993, causing evacuation of the financial center. Officials all but confirmed that a bomb caused the huge blast that left at least five people dead and injured hundreds. (AP Photo/Mike Derer)

Fire, police and other emergency vehicles block the street near the twin towers of New York's World Trade Center after an explosion occurred in the underground parking garage on Feb. 26, 1993. Reflecting on the 10-year anniversary of the bombing, two top law enforcement officials said the nation badly underestimated the terrorist threat to come. (AP Photo/George Widman)

A gaping hole caused by an explosion in an underground garage at New York's World Trade Center reveals various levels of parking beneath the twin towers complex, March 8, 1993. New steel beams were added over the weekend to help shore up the center's shaken foundation. (AP Photo/Richard Drew)

Members of the FBI gather materials from an underground parking garage at the World Trade Center in New York on March 2, 1993. The blast rocked the twin towers complex, killing 6 and injuring hundreds. Investigation clean up continues. (AP Photo/Alex Brandon)

New York City police are pictured during the aftermath of the explosion that rocked the World Trade Center in New York on Feb. 26, 1993. (AP Photo/Ron Frehm)

Firefighters walk past workers installing plywood over broken windows at the World Trade Center in New York on Feb. 27, 1993. At least five people are dead and hundreds were injured as a result of an explosion at the World Trade Center. (AP Photo/Richard Drew)

Nidal A. Ayyad, 25, a chemical engineer arrested in connection with the World Trade Center bombing, is led away by U.S. Marshals at Federal Court after being denied bail on March 12, 1993. (TIMOTHY CLARY/AFP/Getty Images)

Blind Sheikh Omar Abdel Rahman, 49, sits and prays inside an iron cage at the opening of court session in Cairo on August 6, 1989. Rahman, spiritual leader of Egypt's main armed group the Moslem fundamentalist Jamaa Islamiyya, was jailed for life in January 1996 for his role in a terrorist plot against the United States and an assassination bid against Egyptian President Hosni Mubarak. He has also been implicated in the 1993 bombing of the World Trade Center in New York. (MIKE NELSON/AFP/Getty Images)

Visitors peer out across a sunny Upper New York Bay from the 107th floor observation deck of New York's World Trade Center on Saturday, April 17, 1993. The lookout has reopened after being closed for seven weeks following the Feb. 26 bombing at the basement of the twin towers. (AP Photo/Justin Sutcliffe)