OTTAWA, Ontario >> The police in Saskatchewan said Thursday that a stabbing rampage last month in western Canada had been carried out by one man, Myles Sanderson, who killed not just several people on an Indigenous reserve and in a nearby village but also his own brother, Damien Sanderson.

The Royal Canadian Mounted Police raised the death toll to 11 from 10, with Damien Sanderson now counted among the victims.

“Our evidence suggests that Damien did not commit any of the homicides,” Assistant Commissioner Rhonda Blackmore, the commanding officer of the mounted police in Saskatchewan, said at a news conference.

While Myles Sanderson, 32, acted alone in the stabbings, Blackmore said, Damien, 31, was initially involved in planning the killings. She provided no further details about the younger brother’s role.

The commissioner said that investigators had still not determined whether some, or all, of the victims had been targeted, and she added that Myles Sanderson’s motive might never be known.

Police had charged both brothers with first-degree attempted murder and breaking and entering in the attack that unfolded Sept. 4 on the reserve and in the village of Weldon. In total, 29 people were attacked. Eighteen of them were injured, and some remain hospitalized.

The reassessment by the police fits the belief of many members of the James Smith Cree Nation, where most of the victims lived and died. (One man was killed in Weldon.) Many community members say they believe that Damien Sanderson was killed while attempting to stop his brother’s rampage.

Damien Sanderson’s body was found in a grassy area near a house being investigated as part of the attacks on the James Smith reserve. Blackmore declined to say if he had been slain before the other killings started.

Police have yet to construct a full timeline of the killings, and the commanding officer said that such information was unlikely to be released until a coroner’s inquest next year.

But investigators used interviews with 250 witnesses, along with forensic evidence and DNA analysis, to determine that Myles Sanderson had killed his brother, the commissioner said.

Myles Sanderson was arrested after a multiday hunt and a highway chase involving an armada of police vehicles. Authorities said that he had gone into “medical distress” shortly afterward and had been taken to a hospital in nearby Saskatoon, where he was pronounced dead. Blackmore said that his death was still under investigation by the municipal police in Saskatoon.

The killing spree shook the country and turned a spotlight on the province of Saskatchewan, population 1.2 million, and the James Smith Cree Nation, which has more than 3,400 members, with nearly 2,000 living on its reserve.

The commissioner said at the news conference that during the two days leading up to the mass killing, the two brothers had been selling illegal drugs in the First Nation reserve and had been involved in three violent assaults.

At 4 a.m. the day before the killings, Blackmore said, police dispatched two officers from the nearby town of Melfort after a resident of the James Smith reserve reported that Damien Sanderson had stolen a vehicle. Officers were hampered in their three-hour search partly because the most recent photo available of Damien Sanderson had been taken when he was 8 years old, she said.

Two officers eventually found the vehicle in front of a house and questioned three men inside. Unknown to them, the group included Damien Sanderson, who gave the police a different name. Asked if Myles Sanderson had also been a part of that group, Blackmore did not directly reply. She also declined to give any information about what investigators believe happened between that time and the start of the killing spree.

This article originally appeared in The New York Times.