The roots of the massacre reach back to the 1960s, when one of Montreal's most prominent biker gangs, the Popeyes Motorcycle Club, fought their way to dominance under the leadership of Yves "Le Boss" Buteau. Through the 1970s, the Popeyes battled the Devils Disciples and Satan's Choice, campaigns of violence so relentless that journalist Patrick Lejtenyi wrote they "cemented Quebec's reputation as one of the most dangerous places for organized crime to do business in North America." When the Hells Angels absorbed the Popeyes, they inherited that violence along with the territory. But the North Chapter, based in Laval and led by figures like Laurent "L'Anglais" Viau and Yves "Apache" Trudeau, had become a liability. Their reckless drug use and sloppy operations drew heat from police and complaints from partners in organized crime, including the Rizzuto crime family and the West End Gang, who pressured the Angels to bring the chapter under control.

In March 1985, a secret meeting was held in Sorel, Quebec. The leadership of the Hells Angels' other chapters declared the North Chapter to be in "bad standing," a death sentence wrapped in club jargon. The North Chapter members were lured to the Sherbrooke clubhouse under the pretense of a routine gathering. Five men walked into an ambush. Réjean Lessard, commanding 41 men, forced them into the center of a room, where they were shot dead. Three North Chapter members who were present but spared -- Gilles "Le Nez" Lachance, Richard "Bert" Mayrand, and Yvon "Le Pere" Bilodeau -- were ordered to remove the bodies and wash away the blood. Lessard told Mayrand and Bilodeau he was fond of them and gave them a choice: retire from organized crime permanently, or die. Lachance was offered membership in the South Chapter, which he accepted.

The aftermath was methodical. To prove his loyalty to the new order, a North Chapter member named Genest killed Claude "Coco" Roy, a prospect considered close to the murdered men, and handed over five bags of cocaine that Roy had been carrying. Over the following days, the Laval clubhouse was stripped of money, drugs, and six Harley-Davidson motorcycles. Even Yves "Apache" Trudeau, one of the North Chapter's most notorious figures, was not killed as originally planned. He was in a rehabilitation centre when word came that he had been expelled from the Angels. The offer was chilling: rejoin by killing three people Lessard wanted dead. One target was Ginette "La Jument" Henri, the chapter's accountant and the girlfriend of one of the murdered men. The massacre was not a heat-of-the-moment act. It was corporate restructuring carried out with bullets.

The killings were considered extreme even by the standards of the criminal underworld. Salvatore Cazzetta, a well-connected figure who had been expected to join the Hells Angels, found the massacre an unforgivable breach of the outlaw code. Rather than pledge allegiance to the organization that murdered its own, he and his brother Giovanni formed the Rock Machine in 1986. That decision planted the seed of the Quebec Biker War, a conflict between the Hells Angels and the Rock Machine that would consume the province through the 1990s, leaving more than 150 people dead. The Lennoxville massacre, meant to consolidate Hells Angels power in Quebec, instead fractured the province's criminal landscape and created a rival that would challenge the Angels for a decade. Of those convicted for the 1985 killings, Robert "Snake" Tremblay was granted full parole in 2004, Lessard in 2010, and Jacques Pelletier in 2013, though Pelletier was sent back to prison the following year for violating his parole by associating with Hells Angels.