Afghan contractor Shir Ahmad was hired to provide security at an Afghanistan military base, but on Saturday—just 10 days after he was hired—he instead walked up to a group of soldiers and opened fire with an AK-47, killing two. Cpl. Donald Mickler Jr of Ohio, 29, and Pfc. Rudy Acosta of California, 19, were killed, and four others were wounded; three US soldiers responded and killed Ahmad, NBC News reports. Nine US soldiers have now been killed by rogue members of the Afghan security force in the past two months. (More Afghanistan stories.)