Ramzi Ahmed Yousef had been plotting to topple the World Trade Center (WTC) since his arrival in New York in 1992. Ramzi was an explosives expert from Pakistan, but he would need more than these skills to carry out his scheme. Soon, he found himself in the company of people who shared his beliefs. While Ramzi worked on constructing a functional bomb, his co-conspirators examined the layout of the WTC building. For some time, the ingredients for the bomb were kept in a storage room in New Jersey. The final product, a urea-nitrate bomb, weighed a total of 1,200 pounds. Once they were ready, the terrorists rented two vans from a dealership in New Jersey and transported the bomb to the World Trade Cente without being detected. The second van followed the van carrying the bomb as a precaution. It would later serve as their escape vehicle. On February 26, 1993 at 12:17 pm, the bomb went off after the 1,200 pound explosive was placed in the basement of the WTC. Considering that it was a homemade bomb, the explosion was surprisingly destructive. A total of six people died as a result of the explosion, but thousands were injured. The blast, which shut down the building's electricity, left the building unventilated, pitch dark and silent. Tens of thousands of WTC workers and visitors were forced to walk down black smoke filled stairways. There were no lights from 110th floor and below. Amazingly, there was no panic among the evacuees. Firemen, who were working their way up the building, were surprised and encouraging towards the trudging thousands. After a thorough investigation of the area, a number of clues were found that led to the arrest of the terrorists. One of the clues was found in the debris; it was the license plate of the van used to transport the explosive. The authorities were able to trace the license plate to a car dealership in New Jersey. Mohammad Salameh had rented the escape car from the same dealership under his own name. He was arrested upon demanding a refund from the New Jersey dealership after returning the escape van. Following his arrest, the rest of the men involved were also arrested. Ahmad Ajaj, Nidal Ayyad, Mahmoud Abouhalima and Mohammad Salameh were all sentenced to life in prison in 1994. After this tragic incident, the owner of the building, Port Authority of New York and New Jersey, took greater precautions for the buildings security and came into compliance of NYC's safety codes. For instance, it replaced elevators with newer models and upgraded to battery powered lights in the stairway. It even set up additional emergency command centers around the buildings. Unfortunately, these efforts would prove futile on September 11, 2001.