When Ramzi Yousuf and others planned the first attack on the World Trade Centre in New York in 1993, they used a car bomb to attack the structure's weak underbelly.
On February 26 that year, a bomb built into a car was placed below Tower One; the resultant explosion led to six deaths and considerable destruction. Now, the city moves to protect the vulnerable underbelly of Towers Four and Five.
Though the WTC is invariably associated with the two iconic 110-storey towers known as the North and South Towers, the complex had in fact contained seven buildings, the other five much smaller than the Twin Towers. Tower Three was crushed when the Twin Towers collapsed, while Towers Four, Five and Six were damaged beyond repair and subsequently demolished.
Towers Four and Five are now being rebuilt, and the job of protecting its vulnerable underground space has fallen to Jaydev Desai, for whom the brief carries a special significance. 
His son-in-law worked in the WTC, and on 9/11 was late for work when he missed his train. "I am lucky I did not lose my son-in-law in the tragedy," Desai says, adding, "Now I hope to create an environment where people can feel safe."
Security, he says, will be the primary concern not just in the work itself, but even in how he goes about his task.
"I have to shred every document once I have no use for them, or keep them under lock and key," he points out.
A priority is to figure out how every vehicle going into the underground garages can be chemically and otherwise tested for explosives.
Other planned security measures include protection through HVAC (Heating, Ventilation and Air Conditioning), which will incorporate devices that can protect individuals within the building. Oxygen will be released through this device, thus giving the victims time to take stock and make decisions.
The buildings also harness technology capable of protecting the human body up to 130 degrees Fahrenheit.
"The devices cannot be 100 per cent fool proof," Desai points out, adding, "The idea is to eliminate as much loss as possible."
Modern technology can bring security, but there is always uncertainty, explained Desai.
Employed by Liberty Security Partnership, Desai works with 30 other engineering firms, making coordination even more challenging. He teams up with the concerned engineers to review drawings and ensure there is no conflict in the designs.
His selection for the project owes primarily to his design experience with nuclear power plants in Texas and Pennsylvania, and client recommendations.
The resident of Manalapan in New Jersey, who did his bachelor' degree in engineering in Ahmedabad, India, came to the US in 1964.
He continues to straddle both worlds, and is known in India for his work with victims of the Andhra Pradesh cyclone of 1977, the Bhopal gas tragedy of 1984, the Gujarat earthquake of 2001 and other disasters. He has also set up health camps in Ahmedabad and Mumbai for mentally handicapped children, and says his larger goal in life is to help the poor and the needy, for as long as he can.
Setting the WTC conspiracy theories to rest