On the morning of Feb. 26, 1993, a massive truck bomb ripped a hole almost 30 meters (100 feet) across the B-2 level of the parking garage beneath the World Trade Center's North Tower. The blast wave was so powerful that it penetrated five stories of the reinforced concrete building. In addition to causing structural damage, the explosion destroyed or heavily damaged hundreds of vehicles in the garage. That such a powerful explosion killed only six people is nothing short of a miracle, for the attackers had a goal much more grandiose.

They wanted to topple the North Tower onto the South Tower to destroy them both and kill thousands. Had a device of the same magnitude been detonated at street level during rush hour, it would have likely killed scores if not hundreds of people and wounded perhaps thousands more.

From Yemen to New York City

An hour or two after the bombing, I landed in Frankfurt, Germany, on my way back to Washington from Yemen. I was working as a special agent for the Diplomatic Security Service investigating a bombing attack against U.S. Air Force personnel in Aden on Dec. 29, 1992, and a rocket attack against the U.S. Embassy in Sanaa in January 1993. As I stood in the airport terminal looking at the first reports of the World Trade Center bombing, I had no idea the attack was linked to the incidents I had been investigating in Yemen. Later it would be discovered that the same group that conducted the Yemen attacks also bombed the Trade Center: al Qaeda.

I had initially flown to Yemen with a colleague from the explosives section of the FBI laboratory to investigate the strikes against U.S. interests there. We suspected the Libyans might have conducted those attacks after seriously wounding embassy communicator Arthur Pollick in a 1986 shooting in Sanaa and conducting a series of other attacks against U.S. interests around the world.

One of the explosive devices in the Aden attack had failed to detonate, and we wanted to examine it to see if it matched any of the components or bombmaking signatures from devices used in previous Libyan and Libyan-sponsored attacks. However, after examining the Aden device and the manner in which the rocket attack against the U.S. Embassy had been conducted, we were fairly certain the attacks were not the work of the Libyan intelligence service or one of its usual proxies such as the Abu Nidal Organization or the Japanese Red Army, also known as the Anti-Imperialist International Brigade.

But the manner in which those attacks were conducted did tell us one important thing: The CIA had trained whoever had conducted them. Several specific elements of those attacks matched techniques I had learned when I attended the CIA's improvised explosive device training course. (Agents assigned to my office attended the bombmaking course because knowing what is required to make a bomb is crucial when investigating a bombing.) After the CIA station chief assured us that he and his people were not behind the Aden and Sanaa attacks, we concluded that the attackers were most likely Yemenis who had traveled to Afghanistan to fight against the Soviet occupation and had received some training from the CIA's Office of Technical Services — or someone it had trained.

So we knew what the attackers were — jihadists who had returned from Afghanistan — we just didn't have a name for them yet. It would be almost a year before I heard the term "al Qaeda" and several months after that before I realized the term was the name of a group of former mujahideen who fought in Afghanistan and had turned their sights against the United States.

As I watched the newsfeed in Frankfurt, I also had no idea that I would spend the next two years of my life investigating the World Trade Center bombing and the New York Landmarks bomb plot that was connected to it, which targeted the Lincoln Tunnel, the U.N. headquarters and the Javits Federal Building in Manhattan among other locations. In fact, since I was returning from a 10-day investigative trip in Yemen, I figured that if my office was asked to assist in the investigation, my supervisor would assign another agent to the case.

But I was wrong. When I arrived home Feb. 27, I found a message on my answering machine telling me to pack my gear for an indefinite rotation to New York. One of my colleagues had been designated to run the case, but he had become tied down at headquarters handling the myriad investigative leads being sent to regional security officers at U.S. embassies around the world, and he had requested that I be sent to New York to help with the investigation.