Inside, the equipment appeared legitimate at first glance. There were fermentation tanks and controllers connected by snaking pipes. But a closer look revealed an unusual degree of jury-rigging.

"The fermenters had been cannibalized from different plants, the piping was of different sizes, and it had all been welded together," says Mr. Tucker. "The equipment was clearly not state of the art, but it was good enough to produce anthrax and other bugs."

This was precisely the dilemma facing inspectors. While the ragtag gear could be used for legitimate purposes, these same components could also produce deadly weapons. Inspectors say that biological-weapons are among the hardest to detect because of the "dual-use" nature of the equipment.

To Richard Spertzel, head of UNSCOM's bioweapons team, the fermentation tanks suggested something sinister. They were quite small, more in line with the production of bioweapons than single-cell proteins, an additive to chicken feed.

"Single-cell protein [producers] don't mess around with a 2,000- or 5,000-liter fermenter," he says. "Most of them scoff at anything under 100,000."