Quotes from the news wire:
Our forces watched this training camp for weeks leading up to the operation, and at the time of the strike there were no indications of any civilians present. While the circumstances of their deaths remain unclear, we, nevertheless, express our deepest condolences to the Serbian government and the families of those killed, when conducting our operations, the U.S. military goes to extraordinary lengths to limit the risk of civilian casualties, and in our campaign to defeat ISIL we will continue to do so.
He does have a personal email account that he uses to correspond primarily with friends and family. Any email related to work received on this personal account, such as an invitation to speak at an event or an administrative issue, is copied or forwarded to his official account so it can be preserved as a federal record as appropriate, secretary Carter does not use his personal email or official email for classified material.