Over the last 18 months 77 allied troops were killed by Afghans wearing Army or police uniforms — three of them in the past week alone. No Canadians have been among the casualties thus far.
Canadian Maj.-Gen. Mike Day, who is about to end a year-long stint as the second in command of the NATO training mission in Kabul, says every incident has been the subject of intense investigation.
Yet, he says the mystery only deepens.
"God knows, I wish I knew" what is motivating the violence," said Day, who is also the top Canadian soldier in Afghanistan. "It gets four-star level review every time. It captures the full attention of every commander. I would like to say to you that I don't think it'll ever happen again, but I don't think that's realistic."
The possibility of death by treachery has been one of the overriding security concerns for the roughly 6,000 strong training mission, which includes approximately 900 Canadians.
"I'm not trying to sugar-coat this, but it is an ongoing concern that the very people we are here to assist seem to turn on us," said Day, in an interview with The Canadian Press from Kabul.
"We take every single (incident) seriously and we deconstruct it and there is no one single cause."
The motives have varied, that is when investigators can find one. The sometimes enigmatic Afghan culture and language barrier makes it hard to know much any with certainty or fidelity.
There is a small body research in the U.S. that suggests the decades of continuous war and its psychological aftermath could play a part in Afghan troops going over the edge, a theory that receives cautious traction with Day.
"A lot of these guys have been fighting a lot years," he said. "Is it because they've had a bad week or misinterpreted something?"
The Taliban claim credit for all the deaths of coalition troops at the hands of Afghan soldiers — or police. However that is a gross exaggeration because investigators often "don't see the insurgency as the hand behind the trigger," says Day.
The background of some the latest shooters is a Tajik, while another is an Uzbek — both from northern Afghanistan where the Taliban insurgency is loathed more than anything else.
According to published reports in the U.S., American troops have begun taking precautions, wearing light armoured vests under their uniforms whenever they meet with Afghan soldiers or police at base camps.
Day dismisses the notion that cultural tension between free-wheeling Western troops and more socially orthodox Afghans is at the root of the bloodshed.
"I don't buy into this clash of cultures things whatsoever," he said.
There have been reports that NATO is considering whether to enact tighter security procedures, but Day said nothing is imminent and procedures are reviewed all the time.
Afghan recruits go through an eight-step vetting process, which includes verifying identify and criminal background checks. But each of step is tenuous in a country where birth records are hard to track.