Just before the bomb went off, Prem Chhetri spotted something odd.

His job — guarding the perimeter of the Canadian embassy in Kabul — had fine-tuned his senses. And the former Nepalese Gurkha soldier was accustomed to seeing the same woman begging at the same nearby corner every day.

She wasn't there on that morning two years ago — when a blast ripped through the thin-skinned minibus that shuttled Chhetri and his comrades between their heavily fortified compound and the diplomatic mission.

Her absence was the kind of tiny, easily-missed detail that spoke far louder in hindsight to a man who had spent 28 years in one of the world's most renowned fighting formations. Did she know what was coming?

Chhetri may owe his survival to a box lunch that fell off his lap as he was taking the minibus to work that day; when the blast ripped through the side of the bus, he was bending over to pick it up.

"It was my destiny that I survived but I don't know how it was possible," Chhetri told CBC News in a recent interview in Kathmandu, Nepal.

"Deep in my heart, I still feel like I am not alive. I have witnessed my friends dying in front of my eyes. Some had lost their heads and some lost legs."

Prem Chhetri in uniform guarding the Canadian embassy in Kabul prior to the bombing. (Contributed) (CBC News)

Thirteen Nepalese Gurkhas and two Indian contractors were killed in that June 20, 2016 attack, when a suicide bomber belonging to the terrorist splinter group Islamic State-Khorasan Province sprinted up to the bus and triggered the bomb. Sherchan was knocked unconscious.

CBC News has learned that survivors of that attack, and widows of the victims, filed suit against the Canadian government on Tuesday in Toronto at the Ontario Superior Court of Justice.

They allege Ottawa was negligent and failed in its duty to supervise the private security contractor which employed the guards, Sabre International Security.

At the centre of the lawsuit is the question of what steps the federal government took to ensure the Gurkhas were safe on the 10-minute ride — in an unarmoured bus — to and from the embassy, located in a leafy, gated, well-guarded part of central Kabul.

"The attack was a foreseeable consequence of the negligence of Canada and Sabre International Security, including their discriminatory treatment of Nepali and Indian guards," says the statement of claim. "The Nepali and Indian guards were lodged several kilometres away [from the embassy] and were not provided with reasonable protection during their forced daily commute."

These men died in the service of our country and have basically been cast aside. - Lawyer Joe Fiorante, representing the plaintiffs

Neither the survivors nor their family members have spoken publicly until now. Two survivors and four widows agreed to be interviewed by CBC News through a translator.

The contractor is also being sued as part of the same legal action for allegedly failing to honour insurance settlements. The plaintiffs allege the widows have received just a fraction of the $300,000 US they were owed, while the survivors received only $30,000 US of a promised $300,000 fund for health and rehabilitation benefits.

The lawsuit calls on the Canadian government to cover the difference between what they were paid and what they say they were owed and seeks damages for all 20 claimants. They're seeking $20.4 million in combined compensation and damages.

The case is expected to shine a bright light on Canada's handling of private security companies accused of preying on vulnerable migrant workers who take highly dangerous jobs for cut-rate wages.

The Gurkhas killed in Kabul were taking home between $800 and $1,100 per month.

"These men died in the service of our country and have basically been cast aside," said Joe Fiorante, a Vancouver-based lawyer who has fought several international liability cases. He's representing the plaintiffs.

"They were abandoned by our government and we thought that was dishonourable and frankly unacceptable."

Vancouver lawyer Joe Fiorante is representing the survivors of the suicide bombing and the widows of the dead. (CBC News)

Sabre representatives could not be reached for comment. The company's website has been deactivated and emails to its various recruiting accounts, including one in Nepal, went unanswered or were returned.

Shortly after the bombing, Sabre International dropped its contract with the Canadian embassy and left the federal government scrambling to find a replacement.

It is no longer a legal, corporate entity operating in Afghanistan or Iraq. Fiorante said tracking down an address in order to serve court papers has been an exercise in frustration.

"They appear to have disappeared," told CBC News in an interview.

"It raises serious questions about how the Government of Canada contracted with this company."

I felt like death would be easy ... - Man Bahadur Thapa, ex-Gurkha, survivor of the 2016 bomb attack

Global Affairs was asked last week for comment. Despite repeated requests Tuesday, officials did not respond to or answer questions about the selection of the company.

Man Bahadur Thapa, who spent 15 years as a Gurkha, also survived the blast. He still carries pieces of shrapnel in his shoulder and remembers little of the attack.

Thapa said he awoke in extreme pain nearly two weeks afterwards to find himself surrounded by the faces of his distraught family members in a hospital in Delhi.

"I used to cry," Thapa told CBC News. "It was a difficult phase for one and half months. I felt like death would be easy rather than living in that painful way."

Man Bahadur Thapa, a survivor of the Kabul bombing, speaks to CBC News in Kathmadu, Nepal on June 5, 2018. (CBC News)

Staff from the Canadian embassy in India, including the ambassador, regularly asked the Gurkhas recovering in Delhi about their food, housing and working conditions, but the Gurkhas were prohibited by company policy from talking about their concerns, Thapa said.

What the Gurkhas worried about most, he added, was the trip to and from work. Westerners are often shuttled around Kabul in armoured SUVs and military vehicles.

"We had raised the issue of escort and safety since one year of joining [Sabre International] but it did not care," he said.

Some of the guards did speak about their concerns to Deborah Lyons, Canada's ambassador to Afghanistan at the time, Thapa claimed.

The day after that meeting with the ambassador, Chhetri said, the guards were called to a meeting with their commander, who assured them their contracts and insurance were valid.

We were their right hands ... but when we were dying, they did not even bother to see us once. - Prem Chhetri , speaking of Canadian embassy staff in Kabul

Beyond the legal questions, Chhetri expressed bitterness and anger towards the Canadian embassy staff, saying no one from the embassy visited him or the other wounded as they recovered in a Kabul hospital.

"The Canadian ambassador often used to ask us about our problems and regarded us as a family, but nobody came to console us after that big incident," he said.

"We were their right hands, who were always ready to protect them even by sacrificing our lives, but when we were dying, they did not even bother to see us once. They could have at least sent a message through our commander."

The Nepalese government has for two years pressed unsuccessfully to get Canada to compensate the survivors and the widows; at one point it even issued a formal diplomatic note, known as a demarche. Nepalese politicians have publicly accused Canada of negligence and a failure to protect the Gurkhas.

Ottawa, apparently, has remained unmoved.

"There is no employment relationship between the guards and the government of Canada — the guards are employed by Sabre," then-Foreign Affairs minister Stéphane Dion was told in a briefing note, prepared one month after the bombing and obtained by CBC News under access to information legislation.

The contractor was supposed to provide "safe and secure" transportation to the embassy, the note said.

Chitra Kumari Koirala, the widow of Madhusudan Koirala, one of the Gurkhas killed in Kabul. (CBC News)

Chitra Kumari Koirala is a widow of one of the Gurkhas. Her husband, Madhusudan Koirala, spent 17 years in the Nepalese Army and collected a meagre pension, which prompted him to seek out a job with Sabre.

She said she's angry with how the Canadian government has absolved itself of any responsibility.

"Our family was working for their security," said Koirala. "When people are killed on duty, don't they have any responsibility? They [the government of Canada] have to accept that our Nepalese were killed because of their irresponsible behaviour and carelessness. I want them to listen."

Nepalese Gurkhas are acclaimed all over the world for their bravery. They have served in the British Army since the 19th century and view their willingness to work long hours under austere conditions in today's war zones as a badge of honour. It also makes them a prize catch for private security contractors.

Koirala said she begged her husband not to take the job with Sabre. The couple already had endured heartbreak, losing two children — a son and a daughter — in the 2015 earthquake that flattened parts of Kathmandu.

"He patted my shoulder and said he would come back in six months," Koirala said. "He consoled me not to worry about the death of [our] son in [the] earthquake. He said he would love me more and take care of me (his) whole life."

While in Afghanistan, her husband constantly reassured her that he was safe and the only danger was the 10 minute drive.

Part of their last conversation still haunts her.

"He said, 'It's all about luck, so think positive.'"