KABUL - The Afghan who opened fire on a high-ranking delegation visiting a military complex in Kabul, killing US Major-General Harold Greene, had served in the army for three years, an Afghan defence official said on Wednesday.
In the immediate aftermath of Tuesday's attack, the Defence Ministry had described the gunman, who was also killed, as a "terrorist in army uniform", indicating its belief he was an Islamist militant who had infiltrated the army from outside.
While details about the identity of the soldier and his motivation remain sketchy, the fact that he had spent so long in the army before turning on fellow soldiers is likely to be a major line of inquiry in an investigation launched on Wednesday.
"What motivated the shooting is still under investigation, but the shooter was an army soldier, not a terrorist from outside the base," said the official.
Initial findings from the investigation were due to land on Afghan President Hamid Karzai's desk by the evening.
Greene was the most senior US military official killed in action overseas since the war in Vietnam. A German general was also among 14 coalition troops wounded after the man opened fire with a light machine gun.
The attack has raised fresh questions about the ability of NATO soldiers stationed in Afghanistan to train local forces, and will undermine trust between them at a crucial time.
Most foreign soldiers plan to withdraw from the war-torn country by the end of 2014, but, recognising the challenge Afghan forces face in battling a vicious insurgency led by the Taleban, a contingent could remain beyond the deadline in a training and counter-insurgency role.
At their peak in 2012, so-called "insider" attacks threatened the very foundation of the US-led mission in Afghanistan and prompted the coalition to bring in a host of measures to reduce interaction with their local allies.
The number of incidents fell from nearly 50 in 2012 to about 15 last year. "Despite all security measures, such attacks by insiders can never be totally ruled out," a German defence ministry spokesman said.