This article originally appeared on VICE Canada. The plane was late. Canadian Pacific Flight 108, originating in Montreal, was delayed only by a few minutes before it took off from L’Ancienne-Lorette airport outside Quebec City en route to Baie-Comeau. But the bomb that had been placed onboard had been perfectly timed, so when it detonated shortly before 11 AM on the morning of September 9, 1949, the DC-3, with its 19 passengers and four crew, slammed into the bluffs overlooking the St. Lawrence River at Sault-au-Cochon, northeast of the provincial capital, killing everyone. According to the bombers’ plan, the explosive device was supposed to go off when the plane was over water. That would have made proof that it had been brought down impossible to find, and cleared the architect of the mass murder of any wrongdoing.

If everything went according to plan, newly widowed Albert Guay, then only two weeks shy of his 31 birthday, would have been free to marry his teenage mistress. Instead, he, along with an employee at his watch-repair business and the employee’s sister, were hanged at Montreal’s Bordeaux prison. The sister, an eccentric named Marguerite Pitre, would go to the scaffold denying any prior knowledge of the crime.

When Pitre was hanged on January 9, 1953, she would make history as the last woman to be executed in Canada. But, decades later, the evidence that condemned her is hardly ironclad. In fact, it is certainly possible that her version of events was true: She was duped by an evil man into playing an unwitting part in a mass murder.

The story of CP Flight 108 is little known among most Canadians now, but at the time it was a bona fide sensation. It generated international headlines, inspired a movie by one of Quebec’s greatest directors, and remained Canada’s worst air passenger crime until the Air India Flight 182 bombing killed 329 people in 1985.

While Marguerite Pitre’s guilt remains questionable nearly 70 years later, there is little to no doubt that Albert Guay was responsible for the murder of 23 men, women, and children. Born in September 1918, the youngest of five children and supposedly doted on and spoiled by his mother, Guay would grow into a horrible person: violent, abusive, serially unfaithful, self-absorbed, and entitled.

During the Second World War, Guay worked at the Saint-Malo arsenal in Quebec City. Still, in his early 20s, he met Rita Morel, whom he would marry in 1940. In his 1974 book, Causes célèbres du Québec, the late Quebec judge Dollard Dansereau describes Morel as “plump, rather small, with large eyes, a sensual mouth, pretty teeth, and a thick dark mane of hair.” Guay “was of medium stature, rather slim; his face was oval-shaped and pleasant, his manners polite… Also, he owned his own car, a luxury during wartime.”

According to their neighbor, Roger Lemelin, a journalist and novelist who covered the subsequent trial for TIME, they were a happy couple early in their marriage. They were affectionate in public and called each other pet names. After the war, Guay opened a jewelry store in Quebec City. He sidelined in watch repair, despite knowing little about the actual mechanics of timepieces. He hired Généreux Ruest, a man disabled by osseous tuberculosis but whom he would later describe as a “wizard with his hands,” to do the technical work while Guay worked the business end.

The marriage cooled with the birth of the couple’s first and only child, Lemelin would write. There were fights and infidelities and reconciliations, but the warmth had gone. And despite the unhappiness on both sides, divorce was out of the question, thanks to the pervasive influence of the Catholic Church.

Albert Guay and his wife, Rita Morel. Image via Canadian Press

In the spring of 1947, Guay fell in love with Marie-Ange Robitaille. She was 17, and he was 29. He met her while courting another young woman then boarding at her parents’ house, and they began seeing each other soon afterward. They lied to her parents from the outset, with Guay going by a false name and telling them he was still a bachelor.

Their affair carried on for about 18 months, until, in November 1948, Rita Morel, well aware of her husband’s philandering, confronted the Robitaille parents. Mortified, they kicked their daughter out of their house. Luckily for her, her lover had a room lined up: Marie-Ange became a boarder in the home of Marguerite Pitre, the sister of his watch repairman Généreux Ruest, where she lived with her husband and two children.

Guay’s domineering and controlling side exerted itself over Marie-Ange and her new home. She became a virtual prisoner at the Pitre house. He forbade her from traveling or moving back in with her parents, threatened her repeatedly, once vowing to kill them both with a revolver—for which he was arrested—and slapped her on at least one occasion.

But despite the tempestuous nature of the relationship and Guay’s violent outbursts, the affair continued into 1949. In the spring, Guay and Robitaille left Quebec City for Sept-Îles, about 400 miles downriver. It was around that time, it emerged at trial, that Guay decided his wife had to die.

The couple stayed in the small industrial town on the north shore of the St. Lawrence for several months, but by mid-summer, they decided to return to the provincial capital—he to his wife, and she to her parents. But, he told her in a letter, he would soon be free of Rita Morel.

It was obvious to Guay that his wife had to die if he wanted to continue his affair with Marie-Ange. He couldn’t divorce Rita Morel, thanks to the church, but he could kill her. But how to do it, and, more importantly, get away with it?

He asked an acquaintance to poison her but was turned down. (That would-be assassin didn’t bother alerting police at the time.) Eventually, he decided on a bomb. If a bomb detonated on an airplane at the right time, he figured, the wreckage would be would be unrecoverable. No wreckage, no evidence; no evidence, no charges against a suddenly unencumbered widower flush with insurance money and eyes on a young woman not yet out of her teens. The lives of the other passengers and crew were barely considered.

Guay turned to his own in-house wizard, Généreux Ruest, to build the lethal device. The 50-year-old watch repairman would tell the courts that Guay approached him in August 1949, a few weeks before the crime, for help dynamiting rocks on property he owned in Sept-Îles. Ruest agreed, and also agreed to build a timer for the dynamite. He didn’t say or speculate why a precision time-bomb was needed to clear rocks.

Guay got Ruest’s sister, Marguerite Pitre, to buy ten pounds worth of dynamite. She signed for it using a fictitious name, and would also be tasked with bringing the bomb to the airport on the fateful morning of the flight to Baie-Comeau. She cooperated largely because she owed him $600 (roughly $6,000 today), and asked no questions. Once she delivered the package, she testified, the debt would be cleared. That was the arrangement.

According to court testimony, Guay convinced Morel to fly to Baie-Comeau to pick up some items related to his work: jewelry and watches left behind during his months-long sojourn on Quebec’s north shore with Marie-Ange that summer. The couple met that morning at Quebec’s landmark Château Frontenac, where three days earlier, Guay had purchased a Quebec City-to-Baie-Comeau return air trip in his wife’s name and a $10,000 life insurance policy on her, naming him as the beneficiary. A witness testified that on the morning of the flight, Morel appeared reluctant to fly without her husband. The couple argued, and Morel relented. She went on to the airport alone.

Pitre, meanwhile, delivered the package to L’Ancienne-Lorette airport. But Pitre was not a character easily forgettable by those who met her, especially that morning. She’d always been an oddball: She was heavy-set, loud and, according to Dansereau, “of mediocre intelligence.” She was also in the habit of dressing in all black, so much so that her neighbors in the St-Roch neighborhood of Quebec City gave her the nickname of “Madame Le Corbeau” (“Mrs. Raven”).

Shortly before 11 AM, she rushed to the Canadian Pacific counter, arriving out of breath and demanding the package be placed on board Flight 108. She would tell the court that she believed that Guay was sending a statue to a Mr. Plouffe who lived in Baie-Comeau. The investigation would reveal that the address was a fake, and there never was a Mr. Plouffe.

The plane took off just a few minutes behind schedule, with its four crew and 19 passengers, including three children: two babies and a five-year-old boy. Above the municipality of Sault-au-Cochon, witnesses say they first saw white smoke coming from the plane and then heard an explosion. They watched in horror as it plummeted out of the sky and then slammed into the escarpment on Cap Tourmente northeast of Quebec City.

Speaking to a reporter from the Montreal Gazette, CN railway section man Oscar Tremblay said, “It was the most awful scene I have ever come across… They all died outright. There were arms and legs and even heads torn from bodies. There were mangled bodies of little children. The front of the plane seemed to be in one piece, and it was jammed with broken and twisted bodies as if they had been thrown forward in the crash.”

But the plane didn’t explode or burn, and it didn’t take forensics experts long to determine that a bomb in the front left storage compartment caused the crash. Nor was it long for word to get out via the newspapers that investigators were looking for a “mystery woman” who had the package placed on the doomed plane.

Guay was not one to let things take their course calmly. According to her testimony at his trial, on the morning of September 19, ten days after the explosion, he barged into Pitre’s home and told her the truth: The package she delivered contained the bomb. She protested her innocence and ignorance to him, but he was relentless: The best thing for her—for all of them—would be for her to commit suicide and leave a note saying she tried to kill him over the $600 she and her husband owed him.

Guay was arrested on Friday, September 23. Around the same time, Pitre swallowed a handful of sleeping pills and would have died had police interrogators not found her near death in her home. It was during her recovery that she agreed to tell police everything she knew.

In the months following Guay’s arrest, Pitre turned briefly into a weird minor celebrity. Crowds formed outside her building. A cop told a reporter at the time, “People were there like it was a baseball game, pushing, hedging to get a better look at the house and maybe of Mrs. Pitre.” She even began charging photographers who wanted to take pictures of her.

Albert Guay in custody shortly after his arrest. Image via Canadian Press

Guay’s trial began in February 1950. Of the 150 witnesses who were expected to testify, Pitre was among the most important. She stuck to her story, that she believed she was doing Guay a favor in return for expunging a debt, and denied any knowledge that the package she delivered at the airport was anything other than a statue. The Crown prosecutor, wrote a Canadian Press correspondent, “questioned Mrs. Pitre in a loud voice, and Mrs. Pitre shot back in a voice just as loud.”

With Pitre’s testimony, along with Robitaille’s, the forensic evidence, and the insurance windfall all stacked against Guay, it took the jury all of 17 minutes to return a guilty verdict. Judge Albert Sevigny, wrote the CP reporter, “wept” and called Guay’s crimes “diabolical,” and sentenced him to hang on June 23.

But Guay wasn’t going to go down alone.

Généreux Ruest, the bomb-maker, was arrested on June 6, 1950. Police and the Crown doubted his story about building bombs to clear rocks, especially since Guay was spotted at his home on the evening of September 8 and the morning of September 9, asking about the package and testing the timing mechanism.

Guay’s execution was delayed so he could testify at Ruest’s trial in November 1950, but his cooperation didn’t save him. He was hanged at Bordeaux prison on January 12, 1951. The 32-year-old’s last words are said to have been, “Well, at least I die famous.”

His erstwhile employee was also sentenced to death, thanks at least in part to his testimony. It emerged during his trial that he knew the bomb’s target was Rita Morel and that it would go off while en route to Sept-Îles. Though he never admitted to knowingly participating in the plot, he was found guilty on multiple murder charges. Due to his osseous tuberculosis, Ruest was transported to the gallows in a wheelchair and was hanged on July 25, 1952. He was 54 years old.

Guay didn’t testify at Pitre’s trial, though. She was arrested on June 14, 1950, at her brother’s preliminary hearing, initially on charges of intimidating a witness. “She sobbed and shrieked loudly as she was taken by two burly police officers from a corridor near the courtroom and carried to the cells,” according to the Montreal Gazette.

But the case against Pitre was always thin, and Dansereau, the judge, and author, was skeptical of her guilt. He describes her as somewhat dim, a “busybody who took pleasure in being of service to others.” He was also doubtful that Guay would have confided his true intentions to a known blabbermouth like Pitre. But it made no matter: On January 9, 1953, Marguerite Pitre was hanged at Montreal’s Bordeaux prison, becoming the last woman to be executed in Canada.

A last known photo of Marguerite Pitre before her execution. Image courtesy of Kristian Gravenor

Almost 70 years later, with Air India and 9/11 defining the new perils of air travel, the CP Flight 108 tragedy is barely remembered. It was, however, very loosely adapted into a film. Denys Arcand’s Le Crime d’Ovide Plouffe (1984) starred his brother, Gabriel Arcand, as the titular character in the Albert Guay role. But Ovide Plouffe is a very different man. He’s portrayed as a tormented cuckold who falls into the arms of a beautiful French-from-France waitress after learning of his wife’s infidelity. The bomb plot is conjured up by the Généreux Ruest character, who in the film is spurned by Plouffe’s wife. Marguerite Pitre doesn’t feature in it all. A writer named Richard Donovan also based a novel on the crime.

The last executions in Canada took place at Toronto’s Don Jail on December 11, 1962, with the hanging of two men convicted of murder. Lester B. Pearson’s government instituted a moratorium on capital punishment in 1967, and the practice was formally abolished in 1976 by the Pierre Trudeau government. It would remain theoretically on the books under the National Defence Act as punishment for mutiny and treason until 1998. It’s believed Canada executed 710 people, including 13 women, between 1859 and 1962. Pitre was surely one of the last, but her guilt remains far from certain.