Source: Afghan policeman kills 3 Americans July 22, 2012 -- Updated 1918 GMT (0318 HKT) Three Americans were killed by an Afghan policeman, an official says A NATO spokesman says the three were contractors, but did not confirm nationalities Kabul, Afghanistan (CNN) -- An Afghan policeman opened fire at a training center in western Afghanistan on Sunday, killing three Americans, a police official told CNN. The Afghan official, who declined to be named, said the three victims were most probably trainers at the West Zone Police Training Center in Herat province. The shooter was also killed, the official said. NATO spokesman Maj. Adam Wojack said the three killed were civilian contractors working for the International Security Assistance Force. He could not confirm their nationality or what their specific jobs were. The NATO version differed somewhat from what the Afghan official reported. According to Wojack, the gunman was wearing an Afghan army uniform, and one attacker was killed and another fled. The Afghan police official said it was not immediately known whether the attacker had links to any insurgent groups. The motive for the shooting was also unknown. More information will be released Monday, he said. Official: 8 Afghans killed by Pakistan artillery Suicide bomber detonates at Afghan wedding, kills at least 17