When news flashed of an air strike on a vehicle in the Yemeni city of Radaa on Sunday afternoon, early claims that al-Qaida militants had died soon gave way to a more grisly reality.
At least 10 civilians had been killed, among them women and children. It was the worst loss of civilian life in Yemen's brutal internal war since May 2012. Somebody had messed up badly. But was the United States or Yemen responsible?