An officer fatally shot the 16-year-old about 10pm on Saturday after he rushed at police with a large kitchen knife in a Bunning's hardware car park in the southern suburb of Willetton.
In the minutes before he'd called triple-zero threatening "acts of violence" and reportedly sent a text message to multiple people saying: "I am going on the path of jihad tonight for the sake of Allah."
The teen stabbed a man in his 30s in the back outside the hardware store in a random attack that left his victim severely injured.
WA Premier Roger Cook on Monday repeated the state police commissioner's sentiments, saying the stabbing had all the "hallmarks of a terrorist incident".
Asked if WA police would declare the attack a terror incident, Mr Cook said it usually happened when there was an ongoing threat, which wasn't the case.
"The police remain confident that this is a single person acting out of their own volition," he told reporters.
Mr Cook also confirmed that his government and the Education Department were aware of concerns at the boy's school about his radicalised behaviour.
He referred questions about other radicalised students, and claims they may have been attempting to radicalise their classmates, to the Education Department.
"This young man was harbouring some extremist thoughts, which is the reason why he was part of the countering violent extremism program," Mr Cook said.
The boy's text message on Saturday night - which also stated that he was "a soldier of the mujahideen of Al-Qaeda" - prompted multiple concerned calls to police, including from the Muslim community.
Asked if more should have been done to counter the teen's behaviour before the incident, Mr Cook said it wasn't unlawful to have extremist thoughts.
The teen, who was known to police and had mental health and online radicalisation issues, was taken to hospital and declared dead about 11pm.
West Australian Premier Roger Cook says the attack has "all the hallmarks of a terror incident". (Richard Wainwright/AAP PHOTOS)
Prime Minister Anthony Albanese said it was time to support the actions of law enforcement bodies.
"It's the right time to back our police, it's the right time to back the processes that they undertake," he told reporters in Canberra.
"My first thoughts are with the victim, of course in this incident, but also to applaud the very swift action of WA police in acting here.
"(I) acknowledge the very important work that the Muslim community did to alert police to the messages that had been sent out by this young man."
Asked whether the program had failed, WA Police Minister Paul Papalia said working with radicalised people was challenging.
"It is a tough gig to try and change people's beliefs once they've become obsessed and radicalised in this way," he told Seven's Sunrise program on Monday.
"These are people who haven't necessarily committed a crime and you can't lock people up for holding a belief ... That's part of democracy.
"The de-radicalisation effort was being thrown at him - every effort was being made - unfortunately, in this case, it didn't prevent him from doing what he did."
Mr Albanese said the incident highlighted concerns about the content young people could access online.
"One of the themes of a range issues lately involves ... social media, where people can be pushed through the use of algorithms of what occurs towards more extreme positions - is of course a concern," he said.
The WA Education Department has been contacted for comment.
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