as for how i knew to check the x-ray of langdon 's bag ... in light of my realization that langdon was involved in all of this , i had my staff reexamine a seemingly innocuous early-morning call between langdon and peter solomon 's cell phone , in which the kidnapper , posing as solomon 's assistant , persuaded langdon to come for a lecture and also to bring a small package that peter had entrusted to him .