[4][5] The attack was planned by a group of terrorists including Ramzi Yousef; Mahmud Abouhalima; Mohammad A. Salameh; Nidal Ayyad; Abdul Rahman Yasin; and Ahmed Ajaj.

In tapes made after the bombing, Salem alleged that an unnamed FBI supervisor declined to move forward on a plan that would have used a "phony powder" to fool the conspirators into believing that they were working with genuine explosives.

Ajaj tried to enter using a forged Swedish passport, though it had been altered and thus raised suspicions among INS officials at John F. Kennedy International Airport.

After being introduced to his co-conspirators by Abdel Rahman at the latter's Al-Farooq Mosque in Brooklyn, Yousef began assembling the 1,500 lb (680 kg) urea nitrate–hydrogen gas enhanced device for delivery to the WTC.

Dozens of Arabic bomb-making manuals and documents related to terrorist plots were found in Nosair's New Jersey apartment, with manuals from Army Special Warfare Center at Fort Bragg, North Carolina, secret memos linked to the Joint Chiefs of Staff, and 1,440 rounds of ammunition.

[12] According to journalist Steve Coll, Yousef mailed letters to various New York newspapers just before the attack, in which he claimed he belonged to "Liberation Army, Fifth Battalion".

[14] On Friday, February 26, 1993, Ramzi Yousef and a Jordanian friend, Eyad Ismoil, drove a yellow Ford Econoline[15] Ryder van into Lower Manhattan, and pulled into the public parking garage beneath the World Trade Center around noon.

Twelve minutes later, at 12:18 p.m.,[16] the bomb exploded in the underground garage, generating an estimated pressure of 150,000 pounds per square inch (1.0 GPa).

Initial news reports indicated a main transformer might have blown before it became clear that a bomb had exploded in the basement.

The bomb instantly cut off the World Trade Center's main electrical power line, knocking out the emergency lighting system.

[21] A report from the US Fire Administration states that "Among the scores of people who fled to the roofs of the towers, 28 with medical problems were airlifted by New York City police helicopters".

[26] Three tanks of bottled hydrogen were also placed in a circular configuration around the main charge, to enhance the fireball and afterburn of the solid metal particles.

[27] The use of compressed gas cylinders in this type of attack closely resembles the 1983 Beirut barracks bombing 10 years earlier.

Both of these attacks used compressed gas cylinders to create fuel-air and thermobaric bombs[28] that release more energy than conventional high explosives.

Furthermore, Yousef is said only to have considered adding cyanide to the bomb, and to have regretted not doing so in Peter Lance's book 1000 Years for Revenge.

[32] A granite memorial fountain honoring the victims who died during the bombing was designed by Elyn Zimmerman and dedicated on May 25, 1995, on the Austin J. Tobin Plaza, directly above the site of the explosion.

[38] The recovered fragment of the memorial fountain is on display among other artifacts[39] related to the bombing inside the museum's historical exhibition.

[40] Though the cause of the blast was not immediately known, with some suspecting a transformer explosion; agents and bomb technicians from the ATF, FBI, and the NYPD quickly responded to the scene.

A vehicle identification number (VIN), found on a piece from an axle, gave investigators crucial information that led them to a Ryder van rented from DIB Leasing in Jersey City.

The capture of Salameh and Yasin led authorities to Ramzi Yousef's apartment, where they found bomb-making materials and a business card from Mohammed Jamal Khalifa.

[51] The Vista International Hotel at 3 World Trade Center remained closed until November 1, 1994, after extensive repairs and renovations that amounted to $65 million.

[53][54] Also, new security measures were introduced including identification tags for approved cars and drivers, surveillance cameras and a barrier rising out of the roadway to stop rogue vehicles.

As the Port Authority decided to hire Joseph Baum, the restaurant's original designer, to renovate the space at a cost of $25 million reopening was delayed until June 26, 1996.

"[58] Although the FBI received the credit, Diplomatic Security Service (DSS) special agents actually found and arrested Ramzi Ahmed Yousef, the architect of the 1993 World Trade Center bombing.

But Neil Herman, who headed the FBI investigation, noted "The one glaring connection that can't be overlooked is Yasin.

"[61] Daniel Benjamin, a senior fellow at the Center for Strategic and International Studies, writes: "The most knowledgeable analysts and investigators at the CIA and at the FBI believe that their work conclusively disproves Mylroie's claims.

"[63] Among the documents released by the Pentagon was a captured audio file of Saddam Hussein speculating that the 1993 attack on the World Trade Center had been carried out by Israel or American intelligence, or perhaps a Saudi or Egyptian faction.

"[64] Mylroie denied that this was proof of Saddam's non-involvement, claiming that "one common purpose of such meetings was to develop cover stories for whatever Iraq sought to conceal.

"[66][67] Although the 1993 bombing made the World Trade Center a publicly known terrorist target,[68][69] with the possibility of another attack suspected as early as 1995 by FBI Special Agent John O'Neill,[70][71][72] as well as by former Senators Gary Hart and Warren Rudman of the Hart-Rudman Commission in January 2001,[73][74] the 9/11 attacks went largely unforeseen by U.S. intelligence and law-enforcement agencies.

[82] On September 22, 2011, the New York Court of Appeals, in a four to three ruling, excluded the Port Authority from claims of negligence related to the 1993 bombing.