Almost as an afterthought, one realized that the loot which the Nipe stole was seemingly unpredictable. Money, as such, he apparently had no use for. He had taken gold, silver, and platinum, but one raid for each of these elements had evidently been enough, except for silver, which had required three raids over a period of four years. Since then, he hadn't touched silver again.
He hadn't tried yet for any of the radioactives except radium. He'd taken a full ounce of that in five raids, but hadn't attempted to get his hands on uranium, thorium, plutonium, or any of the other elements normally associated with atomic energy. Nor had he tried to steal any of the fusion materials; the heavy isotopes of hydrogen or any of the lithium isotopes. Beryllium had been taken, but whether there was any significance in the thefts or not, no one knew.
There was a pattern in the thefts, nonetheless. They had begun small and increased. Scientific and technical instruments—oscilloscopes, X-ray generators, radar equipment, maser sets, dynostatic crystals, thermolight resonators, and so on—were stolen complete or gutted for various parts. After awhile, he went on to bigger things—whole aircraft, with their crews, had vanished.
That he had not committed anywhere near all the crimes that had been attributed to him was certain; that he had committed a great many of them was equally certain.
There was no doubt at all that his loot was being used to make instruments and devices of unknown kinds. He had used several of them on his raids. The one that could apparently phase out almost any electromagnetic frequency up to about a hundred thousand megacycles—including sixty-cycle power frequencies—was considered to be a particularly cute item. So was the gadget that reduced the tensile strength of concrete to about that of a good grade of marshmallow.
After he had been operating for a few years, there was no installation on the face of the earth that could be considered Nipe-proof for more than a few minutes. He struck when and where he wanted and took whatever he needed.
It was manifestly impossible to guard against the Nipe, since no one knew what sort of loot might strike his fancy next, and there was therefore no way of knowing where or how he would hit next.
Nor could he ever be found after one of his raids. They were plotted and followed out with diabolical accuracy and thoroughness. He struck, looted, and vanished. And wasn't seen again until his next strike.