If you can get past the guards and fences, the ingredients for a chemical attack are available off the shelf at a crumbling military base called Shchuchye in south-central Russia. There, stacked like dusty wine bottles on wooden racks, is a collection of 1.9 million artillery shells filled with nerve agents such as VX, an oily yellow liquid so deadly that a single drop on the skin can kill.
The smallest shells, each containing enough poison for at least 85,000 lethal doses, could be slipped easily into a backpack. But while U.S. officials fret about possible theft, Russia insists that the weapons are secure and that none are missing.
Half a world away, the same kinds of weapons are obtainable in the U.S. chemical capital of Houston, for those savvy and brave enough to attempt the assembly. Last year, a Texas gun enthusiast named William J. Krar was able to legally purchase the materials to make a highly lethal gas called hydrogen cyanide, which he stored at home in a green metal box. Krar might have killed hundreds of people, but a botched package delivery exposed his plans and led to his arrest.
As security officials contemplate the possibility of a chemical attack by terrorists, examples such as these are sources of both concern and comfort. The concern stems from what weapons experts describe as a widespread availability of raw materials for chemical terrorism. The materials include millions of military-grade chemical weapons scattered in at least a dozen countries. They also include vast quantities of hazardous industrial compounds, as well as chemical factories and transports that can be transformed through sabotage into deadly weapons.
Because of the abundance of possibilities, many experts believe the odds for a chemical attack are relatively high, compared with biological or nuclear terrorism. Of the three, the chemical route is widely regarded as the easiest.
"A crude chemical attack is within the reach of any reasonably professional terrorist group," said Jeffrey M. Bale, a senior researcher at the Center for Nonproliferation Studies in Monterey, Calif. "With a sufficiently toxic substance, you will succeed in killing some people."
But whether terrorists could manage a catastrophic attack is another matter, experts say. Somewhat comforting, they say, is the fact that assembling and dispersing deadly chemicals remain complicated and dangerous for amateurs. A review of foiled cases of chemical terrorism shows that the plotters often fall into police dragnets, bungle technical details, or expose themselves to death or injury.
Even a successful release of chemicals, many experts believe, would probably kill relatively few people compared with a sophisticated biological or nuclear attack. The only deadly chemical attack by terrorists in the past decade -- the release of sarin gas on a Tokyo subway in 1995 -- killed a dozen people, not hundreds or thousands, as envisioned by the leaders of Japan's radical Aum Shinrikyo cult.
Terrorist groups such as al Qaeda have professed a desire for chemical weapons, but for now they probably lack the expertise to use them in a catastrophic way, numerous U.S. officials and weapons experts say. As time passes, however, the odds increase that they will try -- and perhaps succeed.
"Fortunately, this kind of thing is hard to do: It requires scientific knowledge, some sophisticated technology and skill," said Joseph Cirincione, director of the Nonproliferation Project at the Carnegie Endowment for International Peace. "The bad news is, it's not hard enough. And you don't know how well these groups have learned the lessons of past failures and improved on them."
Of all the ingenious devices humans have developed for slaughtering one another over 10,000 years, only two have been deemed repugnant enough to merit an outright universal ban. Chemical weapons, together with biological weapons, appear to touch something deep within the human psyche, stirring up feelings of revulsion and fear. Even Gen. Berthold von Deimling, a German field officer who first ordered their use in World War I, found them "repulsive."
Mustard gas, one of a group of 19th-century-vintage weapons known as blister agents, caused the bulk of the deaths and injuries from chemical warfare during the war. In the 1930s, German scientists searching for a better pesticide created the first nerve agents, a class of potent killers that attack the central nervous system. Over the next 50 years, deadly new weapons such sarin, tabun, soman and VX were stockpiled by great powers such as the United States and the Soviet Union and even smaller countries such as Iraq, South Korea and India.
The deep revulsion felt by many toward chemical weapons only increases their appeal to groups such as al Qaeda that seek not to kill troops but to sow fear and panic, intelligence analysts say. After al Qaeda leader Osama bin Laden advocated the use of unconventional weapons in 1998, the group built makeshift chemistry labs at its training camps in Afghanistan. An unclassified CIA report in November said al Qaeda had acquired "crude procedures for making mustard agent, sarin and VX."
Fortunately, al Qaeda appears to have made little progress.
"There are few groups that have both the motivation and the capability to acquire and effectively use chemical weapons," said Jonathan B. Tucker, a senior researcher with the Center for Nonproliferation Studies and author of a forthcoming history of chemical weapons. "Al Qaeda appears to have the motivation but not the capability -- not yet."
U.S. and European intelligence agencies have amply documented the group's failed attempts to master the art of chemical weaponry. Captured training videos from Afghanistan suggest that al Qaeda's amateur chemists succeeded in making cyanide that was potent enough to kill a few dogs. But no traces of the more lethal mustard agent, sarin and VX were discovered in al Qaeda camps.
Last year, British and French police uncovered a series of "poison plots" by al Qaeda-trained groups in Europe, only to find that the would-be attackers were lacking in poison.
In France, a terrorist cell had struggled to manufacture small quantities of a toxin called ricin using kitchen appliances and castor beans.
In Britain, Islamic radicals hatched a scheme to steal osmium tetroxide, an industrial compound that, while hazardous, has never been used as weapon. The plan was foiled, and weapons experts are not convinced that the chemical would have killed anyone.
Still, groups such as al Qaeda could conceivably obtain powerful chemical weapons -- ones with proven ability to inflict truly large numbers of casualties -- by buying or stealing them from military stockpiles. Thousands of tons of nearly pure mustard agent, sarin and VX exist in military depots in such countries as the United States, Russia and Libya. The use of such weapons has been banned since 1925, and the existence of chemical stockpiles was outlawed in 1997. Yet they have never gone away.
For Westerners who have been allowed to see them, Shchuchye's vast rows of wooden shelves lined with VX shells are an unforgettable sight. But the vast arsenal represents less than 10 percent of Russia's 44,000-ton chemical stockpile, and an even smaller fraction of the total quantity of military-grade chemical weapons believed to exist in at least 12 countries.
Defense officials and weapon experts disagree sharply over whether the stockpiles at Shchuchye (pronounced SHOO-shya) and elsewhere are adequately protected. But as recently as the mid-1990s, Shchuchye's commanders could not produce an inventory for the weapons stored there. That frightens arms-control advocates such as Sen. Richard G. Lugar (R-Ind.), who has visited Shchuchye.
"The Russians claim that just one of the shells is potent enough to kill 85,000 people at a football game -- every single person," said Lugar, who for years has pressed Congress for funding to help the Russians destroy the weapons. "There are more than 1.9 million weapons at Shchuchye alone. Anyone who thinks this is not a problem needs to work through that arithmetic."
As recently as this fall, Shchuchye commanders have welcomed delegations of Western visitors to the arsenal to show off the high-tech security system built in recent years with aid from the United States, Canada and Europe. Layers of fences, motion detectors and heavily armed guards control access to the storage barns, located east of the Siberian city of Chelyabinsk, 100 miles from Russia's border with Kazakhstan.
The conditions are dramatically different from those encountered in the mid-1990s by Paul Walker, a chemical-weapons expert with the advocacy group Global Green. In 1994, security consisted of a six-foot barbed-wire fence, bicycle padlocks and an 18-year-old Russian guard who said he had not been paid in months.
"The windows of the storage buildings were broken, and there were holes in the roof," Walker recalled in an interview. "There was obviously no reliable inventory system, because the weapons were spaced haphazardly, with many of the racks only partially filled. When I asked the commander how he kept inventory, he said: 'We keep the doors locked.' "
Even today, Western-style security upgrades are in place in only two of the seven arsenals in Russia where weapons or bulk chemicals are kept. Meanwhile, beyond Russia, far less is known about the security of weapons stocks in countries such as Iran, which used chemical weapons in its war with Iraq in the 1980s and is alleged by U.S. intelligence officials to still possess them.
Nonproliferation experts draw some encouragement from the fact that no stolen chemical weapons are known to have been used in a terrorist attack. Within a few years, the threat will diminish dramatically as Russia and the United States destroy their stockpiles, as required under the international Chemical Weapons Convention. But deadlines for destruction have been pushed back seven years, to 2012, because of financing problems and environmental concerns.
For Lugar, the delay is seven years too long.
"Fortunately, once the weapons are gone, they're gone," he said. "But until that time there's always a danger that something might happen."
Four years ago, a Houston chemistry professor and defense consultant named James Tour set out to prove a point. In April 2000, after arguing in a journal article that terrorists could obtain dangerous chemicals, he had received a stinging rebuke from the Defense Department. "You are so wrong," an agency weapons expert told Tour, according to his account of the conversation. "We monitor every teaspoon."
So Tour went shopping. He first looked up the formula for the nerve gas sarin and then ordered all the ingredients -- on one form, from a single well-known supply company. If assembled, Tour knew, the chemicals would produce about 11 ounces of pure sarin -- enough, in theory, to kill hundreds of people.
The chemicals arrived by express mail the next day.
Afterward, Tour's critics were skeptical, suggesting that his purchase had escaped scrutiny because he is a well-known professor and frequent customer. So a writer for Scientific American persuaded Tour to coach him in repeating the same order, from the same company, only this time in the writer's name.
The chemicals were delivered the next day.
"You can easily get to the point where you're just one step away," said Tour, a professor at Rice University's Center for Nanoscale Science and Technology. "You buy the chemicals, you mix them, and you have sarin."
The second order was placed in November 2001, at a time when police and security officials were on heightened alert after the Sept. 11 attacks. Government and chemistry industry say safeguards have been significantly strengthened since then. Tour, however, is not so certain.
"If I tried it today, maybe it would take three different forms and three different companies, instead of just one. But I have no doubt that I could bypass the system," he said. "And that's if I use domestic suppliers."
An amateur who acquired ingredients for sarin would still face a daunting challenge in attempting to combine the chemicals in the proper sequence without killing himself. But, as the more recent case of Krar illustrates, it is possible to make a powerful poison using readily available chemicals that can be handled safely.
Police describe Krar, 63, as a member of the militia movement, a loose coalition of groups that espouse pro-gun, anti-government and white-supremacist views. Three years ago, after moving to Tyler, Tex., from New Hampshire, Krar began acquiring a large arsenal that included machine guns, dozens of pipe bombs, grenades and a homemade land mine.
But his most unusual weapon was discovered inside a green ammunition box in his home. Inside the box, according to court records, police found nearly two pounds of sodium cyanide and a pair of vials containing hydrochloric acid. Krar would only have to break the vials to combine the chemicals and create highly lethal hydrogen cyanide gas. If released in a crowded room, the gas could potentially kill scores or even hundreds of people, weapons experts say.
Krar was arrested in April and charged with possessing an illegal chemical weapon. He later pleaded guilty. When asked about the origin of the chemicals, he had no reason to lie. He bought them legally, he told FBI agents, from a gold-plating supply store.
The deadliest kind of chemical attack requires no stolen weapons and no mixing of dangerous chemicals. To kill large numbers of people, weapons experts say, terrorists could target any of the hundreds of chemical factories, storage bins, tanker cars or trucks around the country that contain large amounts of lethal gases.
Just as occurred in the 1984 disaster at the Union Carbide pesticide plant in Bhopal, India, a deadly plume of chemicals could travel for miles on the wind and then settle over communities like a suffocating blanket.
Government studies show that casualties from such an event could climb into the tens of thousands or even higher, depending on weather conditions and the chemical involved.
Since the Sept. 11 attacks, the chemical industry has taken voluntary steps to prevent such an attack. Large chemical plants have been studied for vulnerabilities, gates have been fortified, and transport routes have been altered. The American Chemistry Council, which represents more than 2,000 businesses involved in the chemical trade, says its members spent $800 million last year alone to harden facilities against attack. "Following September 11, and without waiting for government direction, ACC members imposed on themselves a mandatory comprehensive security program," ACC President Tom Reilly said in a statement.
Despite the improvements, security experts who have studied the problem continue to list deadly chemical sabotage as a grave threat. Citing EPA "worst case" estimates of casualties from such an attack, a report by the Government Accountability Office in February listed 123 chemical facilities nationwide where a toxic release could affect more than 1 million people. Still, neither Congress nor the White House has enacted measures to require all chemical plants to assess their security and meet minimum antiterrorism standards, the report states.
The failure has no doubt been noted by groups that seek to damage America's economy and demoralize its people. Tucker, the senior researcher with the Center for Nonproliferation Studies, said a conventional attack aimed at a U.S. chemical facility would surely appeal to al Qaeda.
"It would be consistent with the modus operandi of al Qaeda, which has always sought to use our Western technology against us," he said. "Like September 11, such an attack would not be high-tech. But it could be very effective."