So far this story seems bogus. That, or a faulty mobile detector on a cop, perhaps which exaggerated the levels from medical diagnostic equipment.
Could be an empty box with the word radiation or radioactive materials on the side. You find those around medical and biological labs when they throw out the trash. He might have picked up the box to carry something else. The supposedly high radiation count could be bogus.
It is obviously plausible that there is nothing to see here.
Move along.