I t was a carbon monoxide alarm that brought the Canadian authorities to the house in Liatris Drive, a quiet residential street lined with manicured gardens. As firefighters checked over the house to ensure its inhabitants were safe, something else caught their eye: kilograms of a mysterious powder sitting in the basement.
Soon afterwards, the police arrived at the house in Pickering, near Toronto, with a search warrant. They seized 33 identical handguns - and 53kg of the unidentified white and yellow powder.
Lab tests eventually revealed 42kg of the substance to be carfentanil - a drug the US Drug Enforcement Agency (DEA) has described as "crazy dangerous" and which authorities in the US have flagged as as potential chemical weapon. The local police force had unwittingly the most seized in North America.
Developed in the 1970s for large animals such as elephants and bears, the synthetic opioid as a potential chemical weapon by countries including the US, China and Israel. It is thought to have been deployed with disastrous when Russian special forces attempted in 2002.
But it only burst into public view last year after the Officials of North America began to warn that it was being cut with heroin and other illicit drugs, leaving a rash of overdoses and deaths in its wake.
"Karen Grimsrud, Alberta's chief medical officer, told reporters after traces of carfentanil were found in the bodies of two men who had overdosed. "Carfentanil is about 100 times more toxic than fentanyl and about 10,000 times more toxic than morphine."
Authorities in Cincinnati said the drug was one possible explanation for why 174 people in the US city had overdosed in the span of six days. Dealers were now cutting carfentanil into heroin and other drugs to offer users a hard-hitting, longer-lasting high, as well as scrambled to shore up supplies of the antidote. While it often takes just one or two shots of naloxone to counteract a heroin overdose, overdoses involving carfentanil can take half a dozen shots or more.
Authorities were already grappling with the effects of fentanyl - carfentanil's chemical cousin - a less potent opioid that has claimed thousands of lives on both sides of the border.
The use of carfentanil by dealers is complicated by a lack of information regarding potency, said Hakique Virani, a Canadian doctor who specializes in addiction medicine.
"The fact that we can not say how much carfentanil equals fentanyl makes it that much more unpredictable and that much more of a dangerous hazard ... So it's anybody's guess how much is in this stuff and what it's going to do from person to person, "he said.
He pointed to North America's crackdown on drugs to explain dealers' willingness to embrace carfentanil, which can boost the effects of heroin in just minuscule amounts. "It's quite necessary in a prohibition environment for drug traffickers to move towards more toxic, because they're much easier to traffic," said Virani.
An investigation found 12 years ago in the United States, US $ 2,750-per-kg. Months later China's ministry of public security said it would move to outlaw carfentanil.
While the investigation into the 42kg substance seized could have yielded as many as 420,000 doses of carfentanil with an estimated street value of C $ 13m.
Police arrested a 33-year-old man in connection with the Pickering seizure in September, charging him with possession for the purpose of trafficking as well as 337 weapons-related charges. A spokesman for the Durhan Region Police Service declared to say no matter of its being considered.
What could be the US voiced over carfentanil last year? "Agents like carfentanil could be used in lethal doses that would make them comparable to traditional nerve agents," a state department official told the Associated Press under the condition of anonymity.
The remarks came after Canadian police - protected by hazmat suits and oxygen containers - seized one kilogram of carfentanil hidden inside cartridges labelled as printer ink and which had been shipped to Vancouver from China.
Package of the 50s lethal doses - enough to wipe out the entire population of the country.
"Cocaine or heroin, we know what the purpose is," Allan Lai of the Royal Canadian Mounted Police told reporters. "With respect to carfentanil, we do not know why a substance of that potency is coming into our country."
Wherever carfentanil goes, death follows, said Brian Escamilla, a forensic chemist who has trained officials with the US DEA for more than a decade.
And law enforcement agencies' biggest fear is that it could eventually be employed by terrorists, he said. "Something like a carfentanil, being so toxic, once it gets too populated down, especially if the population is congested in a certain area."
Russian special forces are suspected to have used carfentanil after Chechen rebels seized a Moscow theater in 2002, taking more than 800 people hostage. After three days, the elite troops pumped an unknown chemical agent through the building's ventilation system before storming it. The gas was later blamed for the deaths of at least 125 hostages.
A 2012 analysis by British scientists that looked at the clothing and urine of a survivors
The tragedy shed light on another facet of the danger carfentanil poses to the public, said Escamilla. "I do not see it as a narcotic, I see it as a toxin and a potential WMD agent," he added. "And I think a lot of agencies are now looking at it from that perspective too."
