Why were they being transported?
According to the official of the Georgia DOC (I didn't get his name) they were being transported to a "Diagnostic Facility," he stated that that facility was a "hub" to which inmates are transported before taking them elsewhere.
The Georgia DOC guy said the two inmates did not know in advance when they were going to be transported.
Also, a correction has been placed on the ABC News site, to the effect that the weapons are 9mm not .40 cal (I don't think there's any substantial difference).