The nerve agent linked to the Tokyo subway system poisonings is odorless, tasteless and doesn't irritate the skin. But it can kill within seconds if its vapors are inhaled.
Sarin, or what the U.S. Army refers to as Agent GB, is a straw-colored liquid that to date has been developed for military use only, though it has similar properties to commercially produced insecticides such as malathion and parathion.
And, apparently, it is not difficult to manufacture.
"That's one reason they call chemical weapons the poor man's atom bomb," said James M. Allingham, spokesman for U.S. Army's Chemical and Biological Defense Command, headquartered at Aberdeen Proving Ground. "You don't need anything as exotic as plutonium or the complex technology involved for nuclear weapons."
The purer form of sarin, for military applications, "would be a fairly complicated chemical process, but not beyond the realm of doing," Mr. Allingham said.
Gerald G. Watson, a retired major general who was the Army's senior chemical warfare officer, agreed, saying, "There's a lot of literature out there in the public domain on how the reaction is done and what steps are involved."
"Any pretty good college chemistry student could do it, provided that he or she has the proper equipment and the proper facility that would allow a reaction to occur, without the individual being overcome by the vapor itself," said Mr. Watson, now with EG&G Inc., a high-tech equipment company in Huntsville, Ala.
Most of the material needed for such a project "the average industrial countries would have available," he said.
Sarin's forerunner was developed by a German chemist working on pesticides in the early 1930s and quickly picked up by Nazi scientists for possible military use as a nerve agent in World War II.
The U.S. Army manufactured tons of the agent as a defensive weapon during the Cold War, beginning in 1954. Sarin is still stored in aging projectiles and 1-ton containers awaiting eventual destruction at five Army bases in the United States.
Small amounts are kept for laboratory use at the Edgewood area of Aberdeen Proving Ground, Mr. Allingham said.
The liquid has the same consistency as water and evaporates at about the same rate -- but it is deadliest in vapor form.
In military use, sarin would be dispersed into the atmosphere by the explosion of a bomb, rocket or artillery shell containing the material.
The nerve agent acts by depressing an enzyme in the body known as acetylcholinesterase, which is needed to control muscle movements in the body.
Once sarin is absorbed, it attaches to an enzyme that is critical to muscle relaxation, in effect short-circuiting normal muscle control. A victim's muscles stay locked in contracted positions and ultimately, the victim asphyxiates after the respiratory muscles are paralyzed.
Symptoms of exposure to the agent, which affects muscles, glands and the central nervous system, are drooling, excessive sweating, vomiting, diarrhea, weakness, muscle twitching, convulsions and coma.
"A little bit of it can kill a lot of people if it's distributed properly," said Mr. Watson. "In Tokyo, I'm surprised at the relatively few deaths."
The ratio of eight deaths to thousands injured "seems to me to be inconsistent with full-strength GB, but I don't know how it was distributed or what type of ventilation system" was aboard the subway, he said.