"Forensic examination has been done at the scene and we're just putting the pieces together still."
The boy's mother was at the scene on Wednesday night and police have been speaking to her throughout the night.
"I said last night I don't know how a mother gets past losing a son in these sorts of ways," he said.
"But she had friends there to support her and she is certainly assisting police.
"What she saw and the offence that unfolded will play out in the Coroners Court sometime to come."
Commander Fryer said police acted in accordance with their training.
"It was certainly a dynamic situation, they were confronted with a critical incident and they used the options they thought best."
The boy was in year six at Flinders Christian College.
Executive principal Jill Healey said the school was bringing in extra counsellors and chaplains to support students.
Many local schools and churches were helping as well.
"We are well prepared today for caring for the grief that will obviously be in the school community," she told Fairfax radio.
"Support us with love and prayer especially for the family."
Professional standards and the homicide squad are among those investigating.
- AAP