It has been a week like no other for the men and women who wear Canada's military uniform.

On Tuesday, Robert Semrau, a blue-eyed, rock-jawed infantry captain, was demoted and dismissed for fatally shooting a wounded Taliban insurgent. He was the first Canadian to stand trial for a battlefield death that was, by two sworn accounts, a mercy killing.

Then, yesterday, Russell Williams, a colonel who once commanded the country's largest airbase, announced through his lawyer he will plead guilty to two decidedly merciless acts: the sexual assault and murder of two young women.

Both cases sent shock waves through the military, not least because they involved command officers. These were men hand-picked to lead soldiers.

More than any other organization, the military takes leadership seriously.

In the military, leadership confers the ability to command those of subordinate rank; it is the vehicle through which perilous and complex missions are accomplished, sometimes at the cost of life or limb.

Which is why mistakes -particularly of the kind embodied by Williams -cause deep unease at the Department of National Defence.

How could someone so cruel, depraved and criminal be promoted to the senior ranks of the Canadian military? How could a psychopath be placed in a position of command?

"How could we have missed this?" retired Air Force Lt.-Gen. Angus Watt asked on a recent CBC documentary.

"Is there something we did or didn't do that could have given us a clue?"

Watt, who promoted Williams to commanding officer of Canadian Forces Base Trenton, described him as an unusually calm and rational officer who could produce quality work under pressure.

Watt said everyone he's talked to in the military has agreed there was no clue to be found to Williams's dark side.

Others, though, contend the military did not look hard enough.

"You don't become Colonel Williams overnight," retired Canadian Forces colonel Michel Drapeau said.

"He would have had to give signals along the way: his secretaries, his female subordinates. ... Somebody must have been left wondering about him."

Drapeau, a University of Ottawa law professor, called yesterday for a thorough review of Williams's rise in the Canadian Forces. It's important, he said, to understand if that process was flawed, if it overlooked any evidence of Williams's unsuitability for command.

"The military is trying not to see a problem. That has been their approach so far and I say it's wrong."

Prospective military officers, Drapeau said, do not undergo psychological testing of any kind. He believes that should change. At the very least, he said, a psychologist or sociologist should be added to the military panels that interview those being promoted into command positions.

Williams, 47, joined the military in 1987 and enjoyed an ascendant career. He piloted government jets carrying politicians and foreign dignitaries, and once commanded Camp Mirage, a Canadian Forces logistics base in the Middle East.

Professor Alan Okros, deputy chair of command, leadership and management at Canadian Forces College, where officers are trained, said research suggests it is difficult for any organization to identify a psychopath in its ranks.

Okros cited the work of the University of British Columbia's Robert Hare, one of the world's foremost authorities on psychopathology. Hare has demonstrated that psychopaths are often skilled, charming individuals, who are capable of outsmarting psychological tests for abnormal behaviour.

"The suggestion that any organization could identify a clever psychopath using any type of routine interview or assessments is just not plausible," Okros argued.

The guilty plea in the Williams case came during a disastrous week of public relations for the military.

The week began with the revelation that Capt. Nichola Goddard, the first Canadian woman killed in combat, wrote home in 2006 to complain about "six rapes" in one week at a base in Kandahar. The military later said five reports of sexual assault in Afghanistan have been investigated since 2004, but only one has led to a conviction.