A specialized plastic sheeting material used to wrap foods, chemicals, and pharmaceuticals may provide Japanese police with key evidence in their investigation of the March 20 nerve gas attack on Tokyo subways that left 12 people dead and thousands injured. Eleven plastic bags, which were found on trains and platforms within the subway system, have been linked to the terrorist act.
Ten of the bags were found to have contained sarin and all eleven were made of an unusual nylon-polyester compound used in applications requiring resistance to chemicals and gases. Nylon provides resistance to the passage of gas, while the polyester component resists chemical corrosion.
The nylon-polyester material was half-again as thick as the type used to pack food. This thickness of material normally is used only by chemical firms and bag manufacturers that supply them. Because it can be obtained only through manufacturers' representatives and agents, investigators hope to be able to identify individuals other than regular customers who recently purchased the material.
The perpetrators are believed to have brought a solution containing sarin into the subway systems at eleven carefully selected points. To transport the toxic material safely, it was necessary to avoid contact with air. This was the role played by the nylon-polyester material.
For the solution to be activated, the bag would have to be punctured or otherwise breached. One witness reported seeing a man, wearing a surgical mask and sunglasses, repeatedly jabbing a newspaper-wrapped package with his umbrella.
The bags all were irregular in shape, suggesting that they had been cut and sealed by hand using sheets of the material or larger bags. At least one sealing machine was recovered from an Aum Shinrikyo compound raided by police shortly after the attack. No charges have been filed, but police have identified members of the Buddhist group as suspects in the gas attack.
Although police sources released information on the bags and their possible significance to Japanese media, official spokesmen for the Tokyo Metropolitan Police and the National Police Agency were reluctant to provide further details on progress in this aspect of the case.