They threw away the case. Clearly idiots, why would they throw away the case (and probably WITH their fingerprints all over the case) if it’s such an iffy temperature sensitive instrument?
Where does it say that they threw away the case?
Clearly they planned the whole getaway, and that involved not carrying anything that would resemble a violin. If they were concerned (which isn’t perhaps all that likely) about the temperature, it could have left in a backpack; if concerned, perhaps one of those insulated pizza delivery pouches.