If Childs' boss WAS authorized for the information by policy, and Childs honestly felt the boss would misuse the information for something illegal and/or was gunning for Childs, then his actions may or may not be justifiable in this case - he's going to have to produce some proof that his boss had an illegitimate purpose. That could be tough.
Especially considering the City and his (former?) colleagues have had 18 months to doctor and erase the actual evidence that would vindicate Child's. I hope he had copious copies of relevant information tucked away off site.