World Trade Center, 1993 Terrorist Attack
The World Trade Center (WTC) bombing of 1993 has since been overshadowed by the attack that brought the twin towers down on September 11, 2001. Yet, at the time it occurred, the attack loomed as large on the American landscape as the towers themselves once did on the Manhattan skyline. The attack killed six people and injured more than one thousand.
The law enforcement response to the tragedy involved a massive forensic investigation designed to determine the cause of the blast, the identities of those responsible and, ultimately, to ascertain why, although Trade Tower One sustained a great deal of damage, it did not collapse. The forensic sleuthing involved the detailed examination of the blast scene, physical and chemical analyses of samples, and forensic accounting to trace a paper trail that led to the suspects.
At 12:18 P.M. on Friday, February 26, 1993, an explosion rocked the second level of the parking basement beneath Trade Tower One. The explosive material, as forensic investigators would later determine in their chemical analyses of samples retrieved at the site, was somewhere between 1,200 and 1,500 pounds (544–680 kg) of urea nitrate, a homemade fertilizer-based explosive.
The blast ripped open a crater 150 feet (46 meters) in diameter and 5 floors deep, rupturing sewer and water mains and cutting off electricity. Over the hours that followed, more than 50,000 people were evacuated from the Trade Center complex.
The first forensic analysis team to arrive was from the Federal Bureau of Investigation (FBI). The bureau brought in two examiners from the FBI Laboratory Explosives Unit. Over the week that followed, a team of more than 300 law-enforcement officers (including forensic specialists) from various agencies throughout the country would sift through some 2,500 cubic yards of debris weighing more than 6,800 tons.
At the same time that this forensic investigation began, government authorities rushed to protect against physical, chemical, and biological hazards associated with the blast. The explosion had exposed raw sewage, asbestos, mineral wool, acid, and fumes from automobiles. Meanwhile, small electrical fires burned, and pieces of concrete and sharp metal hung threateningly from distended beams.
On Saturday, authorities installed seismographic equipment, cleared the area, and conducted a test run of an empty subway train. The results showed that with a few adjustments, the area could be rendered safe for the operation of the Port Authority Transportation system (PATH) on Monday, thus preventing a virtual shutdown of lower Manhattan. The Environmental Protection Agency and the Occupational Safety and Health Administration began taking steps to clean up biological and chemical debris.
Meanwhile, the forensic investigation expanded, with two chemists each from the FBI, ATF (Bureau of Alcohol, Tobacco, and Firearms), and the New York Police Department collecting and studying residue from the blast area. In the course of this work, investigators found a key piece of evidence: a 300-pound (136-kg) fragment of a vehicle that, based on the damage it had sustained, must have been at the epicenter of the blast. Sewage contamination had rendered it unusable for residue analysis, but recovery of a vehicle identification number allowed the vehicle to be traced.
Authorities traced the vehicle to a Ryder truck rental facility in Jersey City, New Jersey, where it had been reported stolen. On Monday, while FBI special agents were at the Jersey City facility to interview personnel there, a Ryder clerk received a call from a man identified as Mohammed Salameh. The latter demanded the return of his $400 deposit for the van in question, and the Ryder clerk arranged for him to return and collect the deposit on March 4, 1993. When Salameh arrived, he was arrested.
A search of Salameh's belongings led investigators to Nidal Ayyad, a chemist working for the Allied Signal Corporation in New Jersey. Forensic accounting of toll records and receipts helped lead to a safe house in Jersey City, New Jersey, where authorities found traces of nitroglycerine and urea nitrate. They also uncovered evidence that Salameh and Ayyad had obtained three tanks of compressed hydrogen gas. In the course of searching a storage room rented by Salameh, investigators found large caches of urea, sulfuric acid, and other chemicals commonly used in making bombs. On March 3, the New York Times received a letter that claimed responsibility for the bombing. A subsequent forensic investigation of DNA samples matched Ayyad with the saliva on the envelope flap.
A forensic investigation was conducted to examine how such a massive blast failed to collapse the tower. The consensus opinion is that the location of the explosion, on the second level of the underground parking lot, acted to diffuse the intensity of the explosion. When the concrete floor of that level ruptured, much of the force of the blast was directed downward into the lower levels of the parking garage.
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