CNN
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Investigators now believe Myles Sanderson was the only killer in a mass stabbing attack in Canada’s Saskatchewan province in September – and his brother, initially named a suspect, was among those he killed, police said Thursday.

That means 11 people were killed – not 10 as previously announced – in the attacks in or near northern Saskatchewan’s James Smith Cree Nation, an Indigenous community, Royal Canadian Mounted Police said Thursday.

And it’s a major reversal on authorities’ view of Sanderson’s brother Damien Sanderson, who investigators initially said was a suspect along with Myles Sanderson as police responded to the stabbings on September 4.

The killings captivated Canada for days as authorities searched for the pair. During the manhunt, Damien Sanderson, 31, was found dead September 5 near a house on the James Smith Cree Nation reserve. Myles Sanderson, 30, was arrested September 7 after a vehicle chase in Saskatchewan and died later that day after experiencing “medical distress,” police said.

While authorities still are investigating events leading to the stabbings, they “believe it’s important to clarify Damien’s involvement,” the RCMP said Thursday.

“After completing 250 interviews, processing over 670 exhibits, reviewing and following up on over 100 … calls for service, investigators have determined … Damien Sanderson was a victim of homicide by Myles Sanderson,” an RCMP statement reads.

“Myles Sanderson committed all the homicides alone,” the statement reads.

Police have not said how or when Damien Sanderson died. On the day his body was found, police said he had injuries that were not believed to be self-inflicted.

While investigators no longer believe Damien Sanderson killed anyone, they have determined “Damien was involved in the initial planning and preparations for the attacks.”

“We are still investigating the extent of Damien’s involvement,” the RCMP statement reads.

Investigators are trying to get “an accurate picture of the motives behind these crimes and why some of the victims were targeted,” the RCMP said Thursday.

“This will take time to complete and the reality is, we may never really know exactly why,” the RCMP said.

In addition to the 11 killed, 18 others were injured in a spree of stabbings that spanned numerous crime scenes September 4 in the Indigenous community and a nearby rural village, authorities had said.

In the hours after the attacks, police said both brothers were suspects, and that investigators believed they were traveling together in a vehicle.

By September 7 – the day Myles Sanderson was captured and died, and two days after Damien Sanderson was found dead – a reporter asked RCMP Assistant Commissioner Rhonda Blackmore whether Myles Sanderson was the one who carried out the killings.

“Our witness accounts that we have received have indicated that Myles Sanderson was the person responsible,” though she noted the investigators still were trying to confirm exactly who was involved.

In Thursday’s statement, though the RCMP said it still didn’t have a full understanding of the motive, it said that both brothers “were involved in at least three violent altercations involving other individuals in the James Smith Cree Nation” before the killings.

“None of these violent altercations were reported to police prior to the homicides being committed” on September 4, the RCMP said.