Lee Bonneau was found injured in a wooded area last month not far from the Kahkewistahaw First Nation community centre where he was last seen.
Staff Sgt. Larry Brost told a news conference Tuesday that the person investigators feel is responsible for the killing is another boy under the age of 12, who is too young to be charged under the Youth Criminal Justice Act.
"If we thought that somebody would have been responsible for this death outside of this child, that person would have been arrested, charged accordingly and there would be a court date set. However, that's not the case here," Brost said in Regina.
"This is a child."
"There's no other person at this point in time in the investigation that could be responsible for this other than this child," he added.
Authorities have said Lee, who was not a member of the First Nation, was in the care of the Ministry of Social Services. His foster home was just off the reserve, where his foster mother had gone to play bingo.
Lee was last seen walking with the older boy outside the reserve's recreation complex.
RCMP received a report that Lee was missing at about 10 p.m. on Aug. 21. He was found about 20 minutes later.
Lee died in hospital from head injuries that police say were consistent with an assault. Brost said "something of opportunity" was used as a weapon.
"We are still looking towards what was used in that assault. We believe it was a weapon, certainly not a knife or a gun, but we are examining possibilities and using forensics to determine that," he said.
Brost said the young suspect, who is from the reserve, was known to police before the killing, but the officer refused to elaborate citing privacy legislation.
The two children did not know each other, he said.
The child responsible for the death is now in the custody of the province.
Social Services spokeswoman Andrea Brittin said the ministry will focus on the boy's treatment and on the safety of the community.
"He is a child in need of protection and it is our responsibility to ensure he receives the treatment that he requires," Brittin said. "Those treatment needs are going to change as he grows older."
Saskatchewan does not have a secure facility — one where doors could be locked — to hold the boy. Only Alberta, Ontario and Nova Scotia have closed-custody type facilities for children under 12.
However, Social Services Minister June Draude said the boy is under 24-hour supervision.
"We are constantly monitoring him on a very, very regular, regular basis. If we feel that there's even a little bit of a chance that more should be done, I've told them that I want to be notified immediately," said Draude.
"We do know that we've checked with other jurisdictions to see if we can be working with them. We've reached out to directors right across Canada and said, 'If we need further help can we get it? They said yes."
Draude has also asked Saskatchewan children's advocate, Bob Pringle, to do an immediate review of the case. She said she hopes the review will help gain some understanding of how this could have occurred and what, if anything, can be done to prevent another such tragedy.
Brost said it may never be clear why Lee Bonneau was killed.
"Why things like this actually happen and why events like this turn out the way they do, this is something that we hope to arrive at," said Brost.
"However, quite often the case —_ and this is a unique case — we may never find that answer."
The case has raised questions about the age at which someone can be held responsible for a crime.
Neil Boyd, a professor and director of the school of criminology at Simon Fraser University in British Columbia, says ages for responsibility are set for many things, such as driving, drinking or voting.
"Under the age of 12, we're saying, essentially as a society, we're saying that this is a person who doesn't have the emotional or intellectual maturity to be held responsible, doesn't have the free will, if you like, to be held responsible for this kind of action," said Boyd.
Boyd, who has been a criminologist for 35 years, says that children killing children is unusual in Canada.
"We hear of this kind of thing happening in the United States a little more frequently, typically involving firearms and accidental discharge of firearms," he said.
"But the killing of one child by another child under the age of 12 is, fortunately, a very rare event."
In 1995, an eight-year-old boy was too young to be charged for his alleged role in the killing of Johnathan Thimpsen, a seven-year-old from the northern Saskatchewan community of La Ronge.
Court heard how the boy, who wasn't named publicly, worked with 14-year-old Sandy Charles to lure Thimpsen into the woods. Thimpsen was stabbed and his body mutilated.
Charles, who was tried for first-degree murder as an adult, was a fan of the horror film "Warlock" and admitted to killing in the belief that drinking the rendered fat of a young virgin would give him the power to fly. He was found not guilty by reason of insanity.
A girl from Medicine Hat, Alta., was convicted in the 2006 murder of her parents and brother when she was 12.
Court heard the girl, who cannot be identified under the Youth Criminal Justice Act, and her 23-year-old boyfriend, Jeremy Steinke, committed the murders because there were angry at her parents for disapproving of her relationship.
One of the most high-profile cases internationally happened in the United Kingdom.
In 1993, two-year-old James Bulger was abducted from a shopping centre in northern England and beaten to death by Jon Venables and Robert Thompson, who were both 10 years old at the time.
Thompson and Venables were convicted of murder and spent eight years in youth custody. They were released in 2001 with new identities.
Note to readers: This is a corrected version. A previous version had Britten.