As a dog owner myself (currently out walking mine just now) this is just horrible.
First instinct is to shout BASTARD at the cop and then hope he gets jail time but when you step back and take a moment to reflect its just a tragic accident and I bet the cop is absolutely devastated.
Some sort of of community service at the dog shelter or something like that, is what I would do or get him to go out and teach the kids in schools.