The 16-year-old boy, described as "Caucasian", was known to the police. Col Blanch, the police commissioner of the state of Western Australia, said the boy had mental health issues and had been part of a police deradicalisation programme. Speaking at a news conference, state premier Roger Cook said: "There are indications he had been radicalised online. But I want to reassure the community at this stage it appears he acted solely and alone.