On Monday, his 31-year-old brother Damien Sanderson had been found dead in a grassy field in the Cree community.
Authorities said he likely had been killed by his older sibling, who remained a fugitive until his arrest near the town of Rosthern in Saskatchewan -- about 100 kilometers (60 miles) west of where the stabbings occurred.
Blackmore said that with both brothers now dead, "we may never have an understanding of (their) motivation."
The manhunt had stretched across three provinces, and gone from Regina, Saskatchewan province's capital 300 kilometers to the south, and then back to the James Smith Cree Nation -- in response to reported sightings.
An AFP reporter at the scene near Rosthern on Wednesday saw several police cars surrounding a white pickup along the side of a highway.
An hour before the arrest, police issued an alert about a man armed with a knife in a stolen white Chevrolet Avalanche nearby, making a link to the stabbing case and urging locals to shelter in place.
Blackmore said police, after receiving an emergency call about the theft, spotted the speeding vehicle and "directed (it) off the road and into a nearby ditch."
"He was arrested by police and taken into custody," she said. "A knife was located inside the vehicle."
It was a dramatic end to a four-day manhunt across the vast Prairies region.
It also offered relief to a nation distressed by one of modern Canada's deadliest incidents of mass violence.
"Our province is breathing a collective sigh of relief as Miles Sanderson is no longer at large," Blackmore commented, adding that now the families of victims and the community "will be able to start healing."
Myles Sanderson had a history of explosive violence that led to 59 past convictions, and was also wanted for breaching parole in May after serving part of a sentence for assault and robbery.
But with no known motive for the latest attacks, relatives of victims spoke out earlier Wednesday about their "nightmare" and called for answers from authorities.
Mark Arcand said the killings that claimed the lives of his sister Bonnie Burns, 48, and her son Gregory Burns, 28, were a "horrible, senseless act."
"We're broken," he said, describing emotions of anger and sadness. "It still feels like it's a nightmare. It doesn't feel real."
"How did this happen to our family? Why did it happen? We have no answers," he told a press conference. "We just know that our family members were killed in their own home, in their yard."
Arcand recounted how his sister had rushed out of her house to help her son, who was bleeding out in their driveway after being stabbed several times.
"She was stabbed two times, and she died right beside him," he said. "She was trying to protect her son."
A neighbor ran over to try to stop the assailants, but she too was killed, he said.
The family and the community, Arcand added, has "a steep hill to climb, and we're going to climb it together, united."
The coroner has released the names of the deceased victims -- six men and four women aged 23 to 78 years old.
All but one were members of the Cree community. The other was a widower who lived with his adult grandson in nearby Weldon.
Seventeen adults and one young teen were also wounded in the attacks, police said. Among them was another son of Bonnie Burns who was slashed in the neck.
Ten people remain hospitalized, including two in critical condition, according to the Saskatchewan Health Authority. Seven others have been discharged.
Police believe some of the victims were targeted and others were attacked randomly.
The grisly attack followed several recent mass killings across Canada. A gunman masquerading as a policeman killed 22 people in Nova Scotia in April 2020, two years after a driver of a van killed 11 pedestrians in Toronto.
Another shooter killed six worshippers at a Quebec City mosque in January 2017.