Is there any reason they could give that would mitigate their actions? Where we would say, "Yeah. OK. Now I understand why they did it."
Why even ask the question? Better yet, why should they answer it?
Really. Why ask why? All you will get is evasive eyes and an "I dunno". Kids are stupid, some stupider than others, and they do stupid things. Some times those stupid things are criminal and they get caught.
No helping it. Sixteen hours of mandatory classroom instruction on not throwing turkeys off of overpasses is not going to solve this problem. It just doesn't make any sense.
What you can do is convict and punish the guilty. Remove them from a position to harm innocent people and provide and example to others. It's not much, but it is something.