Myles Brandon Sanderson was born around 1990 in Saskatchewan, Canada. He grew up within the James Smith Cree Nation and had a long-standing history of violence, addiction, and crime. From a young age, Sanderson was exposed to substance abuse, beginning cocaine use as early as age 14. Over time, he became deeply entrenched in cycles of rage, violence, and criminal behavior.

Sanderson's criminal record was extensive. He accumulated 59 convictions across 47 criminal cases, ranging from assault, robbery, and mischief to assaulting a police officer and making threats. Despite these red flags, he was released on statutory parole in August 2021, having served part of a five-year prison sentence.

Authorities had been searching for him since May 2022 after he failed to report to his parole officer. He was under a lifetime weapons ban and prohibited from using drugs or alcohol, but he repeatedly violated these conditions.

On September 1, 2022, Myles Sanderson returned to the James Smith Cree Nation to sell cocaine. The following day, he assaulted his partner and attempted to run her over with a car, an attack that triggered intervention from his brother, Damien Sanderson. The brothers went on to spend the next two days selling drugs, drinking, and assaulting individuals, including Gregory Burns, who would later be killed during the massacre.

By early morning on September 4, 2022, Myles and Damien had been driving around, reportedly "pumping themselves up" for something. At approximately 5:30 a.m., they entered the home of Damien’s wife searching for her. After failing to find her, Myles stabbed a man in another home. Damien intervened, stopping the attack, but shortly after, a violent confrontation broke out between the brothers. Damien fled, severely wounded, into a nearby wooded area where he would later be found dead.

Myles then embarked on a solo killing spree, moving house to house across the James Smith Cree Nation, targeting both relatives and strangers. In less than three hours, he killed ten people and injured multiple others. He stole vehicles, attacked his former in-laws, including Earl Burns Sr., who attempted to pursue him with a school bus but died after crashing it. At around 6:53 a.m., Sanderson returned to a home he had previously attacked and killed two more victims, one of whom had returned to help.

After committing attacks in 13 separate locations, Sanderson drove to the village of Weldon, where he murdered 78-year-old Wesley Petterson at approximately 8:19 a.m. The massacre would later be declared one of the deadliest mass killings in Canadian history.

Police were first notified of the stabbings at 5:40 a.m. Emergency alerts were issued across Saskatchewan, and later expanded to Alberta and Manitoba. Despite the sweeping manhunt, Myles managed to evade authorities for three days.

On September 7, 2022, he was spotted driving a stolen Chevrolet Avalanche near Wakaw, Saskatchewan. Police used a PIT maneuver to force his vehicle off the road at 3:28 p.m. near Rosthern. Sanderson was apprehended alive but quickly entered medical distress. He was pronounced dead shortly afterward. An autopsy confirmed he had died of an acute cocaine overdose.

On October 6, 2022, the RCMP confirmed that Myles Sanderson acted alone in the murders, including the killing of his brother Damien. Although Damien had been part of the planning stage, he did not carry out any killings. The motive behind the spree was never fully understood, but it was believed to be linked to a mix of drug abuse, paranoia, family grievances, and a complete mental breakdown. A total of 12 people died, including Sanderson himself. Seventeen others were injured.