The ingredients in the deadly terror bomb that blasted the Alfred P. Murrah Federal Building in Oklahoma City are so easy to obtain that almost anyone could make a lethal explosive, posing virtually insoluble problems for law enforcement, experts said.
Federal investigators at the scene disclosed that the principal chemical in the bomb -- apparently carried in a car or truck -- was ammonium nitrate, an extremely stable nitrogen compound widely used in fertilizers. It explodes violently when packed in a tight container and detonated electrically.
The same compound, loaded into a rented van and mixed with diesel fuel, was the key ingredient in the bomb that killed six people and injured more than 1,000 when it exploded in the underground garage of New York City's World Trade Center two years ago.
Ronald Atkins, chief of explosives research at the Lawrence Livermore National Laboratory in California, would not discuss the specifics of the Oklahoma City bombing, but he said the heavy explosives available anywhere in the world today are so simple that "they're something that a high school kid could cook up."
And although scientists have developed a variety of exotic devices for sniffing out lethal chemicals in car bombs, anti-terrorism specialists acknowledge the bitter truth that the systems can only be used when vehicles are moving very slowly or are immobilized at choke-points, such as inspection stations, garages or loading docks.
Since World War II, the technology of explosives has become more and more sophisticated, but nitrogen compounds are the crucial ingredients of virtually every device. The nitrogen compounds that terrorists mix into their biggest bombs are extremely crude.
At the federal Office of Technology Assessment in Washington, Anthony Feinberg, the agency's expert on terrorist explosives, said a combination of ammonium nitrate and fuel oil is the "classic mixture" that Middle Eastern terrorists have used in their attacks.
A suicide driver rammed such a brew into the U.S. Marine compound and the American Embassy in Beirut in 1983, killing 241 Marines as they slept.
"Those explosives are really impossible to detect in advance, except through intelligence operations or informers," Mr. Feinberg said in an interview. "And dogs are still probably the best way of sniffing out bombs."