Even before placing the phone call, he could have asked both of the pair to show some kind of picture identification; they drove to the plant, so at least one of them should have a driver's license. The fact that they had originally given phony names would have been immediately obvious (a professional would have come equipped with fake ID, but these teenagers had not taken that precaution). In any case, Leroy should have examined their identification credentials and written down the information. If they both insisted they had no identification, he should then have walked them to the car to retrieve the company ID badge that "Tom Stilton" claimed he had left there.