Agreed. I have no problems with punishing the guy for the criminal destruction of private property if it applied in this case. But I would ask you this: Who did this man wrong? Did he wrong the inmate, the cats, or just our sensiblities? Was the inmate allowed to have cats? If there was a rule that no pets are allowed, then the inmate had no power of disposition over the cats. Were the cats wronged? Impossible, because cats don't have "rights". So really, that leaves our sensiblities as what suffered the wrong. My sensiblities suffer all the time, but the law should't allow me to receive compensation every time I'm outraged about something.
And MaggieMay is right that something is criminal pretty much whenever the legislature passes laws saying it is, your property or not.
I can't argue with that. I might think the legislature is goofy passing such laws, but even bad law is law nonetheless. But I must add that legislating a standard of "deviancy" and "cruelty" is a slippery slope at best.