Matter of the Dematerializing Armored Car

In The Matter of the Dematerializing Armored Car, Chief of Detectives Heinz Noonan is asked to solve the disappearance of an empty armored car and its two drivers from a tunnel with guards on both ends. Why would anyone want to steal an empty armored car and is it linked the $12 million in cash in the armored car vault under the control of the United States Department of Treasury which vanishes wi...