Interesting passage that I found on Wikipedia regarding dry ice:
California law defines "destructive device" as a type of weapon, including "any sealed device containing dry ice (CO2) or other chemically-reactive substances assembled for the purpose of causing an explosion by a chemical reaction."[31] However, dry ice bombs operate not via chemical reaction but via a simple phase change. The approximate volume of carbon dioxide gas produced by sublimating a known mass of dry ice can be calculated using the Ideal gas law. While dry ice bombs are not explosive devices per se, when the container bursts, it releases plastic shards that can injure an unprotected person.
So a good defense lawyer will argue that this was not a "destructive device" by definition.