Dr. Kessler said inspectors from his agency had detected a manufacturing problem at a Warner-Lambert plant in Puerto Rico.

But inspectors cannot always detect contaminated meat just by quickly smelling or looking for the obvious signs of spoilage.

The inspector could not detect signs of intoxication, Mr. Oberstar said, and believed he had no authority to intervene and let the plane depart.

The inspectors who showed up that day in 2000, however, apparently never detected the hundreds of sham files, according to state records.

It also deepened suspicions by reporting that inspectors had detected traces of highly enriched uranium at an Iranian nuclear facility.

But inspectors can detect the special manufacturing needed to create fuel for nuclear weapons.

Dr. Fisher, who is a leading expert on bridge failure, said that inspectors often do not detect the corrosion because it occurs beneath the surface of the steel beam.

Maybe the inspector detected the pride of ownership in Steve's expression, for he quickly demanded: "Did you bring this here?"

Infrared images allow inspectors to detect any faulty construction, problems with ventilation, leaks, water intrusion and so on.

In their last visit, in January, the inspectors did not detect any illegal weapons activity there.