A plot by a Blackburn teenager to attack an Anzac Day parade in Australia would “in all probability” have caused a number of deaths if it had not been stopped, a court has heard.
At a two-day sentencing hearing, Manchester Crown Court heard the boy encouraged a Melbourne man to behead police officers at a parade in April.
He had previously threatened to cut the throat of his teacher, the court heard.
The 15-year-old has pleaded guilty to one count of inciting terrorism.
The teenager, who cannot be named for legal reasons, is thought to be the youngest Briton guilty of a terror offence.
He was radicalised over the internet by Islamic State propaganda, and formulated the plot “from the bedroom of his parents’ suburban home”, prosecutor Paul Greaney QC said, outlining the case.
Anzac Day, held on 25 April each year, commemorates the Australian and New Zealand Army Corps’ World War One battle in Gallipoli, and this year marked its centenary.
The Lancashire teen sent thousands of online messages to an alleged Australian jihadist named Sevdet Besim, including one suggesting he get his “first taste of beheading” by attacking “a proper lonely person”, the court heard.
“There is no doubt” the pair planned to carry out the attack, and also made references to the production of a martyrdom video to use for propaganda purposes, Mr Greaney said.
“In the event, fortunately, the authorities here and in Australia intervened and a plot that would in all probability have resulted in a number of deaths was thwarted.”
The court was told a well known Islamic State recruiter – Abu Khaled al-Cambodi- had instigated contact between the defendant and Mr Besim.
Mr Greaney said: “That such a significant Isis (IS) figure put the two in touch is of itself indicative of the serious nature of the plot upon which (the defendant) and Mr Besim were to embark.”
The Muslim defendant was “undoubtedly a troubled young person” who had had a “difficult” upbringing and was regularly excluded from school, Mr Greaney said.
He was said to have “strong religious convictions” and was disruptive when he attended a large secular school where most of the pupils were white, the court was told.
On one occasion he praised Osama bin Laden and stated his own desire to become a jihadist and a martyr, the court heard.
The defendant was later referred to the government’s counter-extremism programme Channel after his mother explained to the school that he “spent time talking over the internet to persons that he had not met.”
After he was moved to a new school, he threatened a male teacher, saying he would “cut his throat and watch him bleed to death”.
Another male teacher logged a comment from the youngster that he was plotting to kill someone, the prosecutor said.
In 2014, he pushed his phone into the face of a teacher, which the court heard was playing a video showing dead and bloody bodies on the floor.
Mr Greaney said: “He also spoke of his desire to be a suicide bomber, stating that if he had to choose where to detonate his bomb it would be on a plane in order that he could maximise the fatalities.”
In one class he was reported to have said to a teacher: “You are on my beheading list”.
A second referral to Channel took place in November 2014 but the youngster allegedly continued to threaten to kill teachers. He also reportedly described the Charlie Hebdo attackers as his heroes
In one lesson on the death penalty alongside the comment “killing another person is immoral”, he had written: “You could not be more wrong”, Mr Greaney said.
The sentencing hearing is expected to conclude on Friday.