Police in Edmonton say a 16-year-old boy who shot and killed two officers a week ago had been apprehended in November under the Mental Health Act and taken to hospital for assessment.
Police also say the same gun was used in a shooting days before the killings at a nearby restaurant that left a man injured.
Police say detectives are working to trace the origins of the gun and how it came to be in the boy's possession, and that other people could face charges.
Police say the employee at the Pizza Hut, who was shot and injured March 12, remains in hospital in stable but critical condition.
Constables Brett Ryan, 30, and Travis Jordan, 35, were responding to a family dispute at a northwest apartment complex on March 16 when they were shot at multiple times.
Police say the boy also shot and wounded his mother during a struggle for the gun before shooting and killing himself.
Police say the youth's mother remains in hospital in critical but stable condition and is unable to speak but has been able to communicate through writing.