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A 15-year-old British boy who came within days of successfully plotting an Anzac Day parade “massacre” in Melbourne after being radicalized by ISIS has been sentenced to life in jail.

The teenager, from Blackburn in northwest England, sat expressionless flanked by his teary parents as Judge John Saunders told Manchester Crown Court the youth remained a significant danger to the community.

“I have given this matter very careful thought because of the consequence so passing a sentence of detention for life on someone of (boys) age but I have a duty to protect the public,” the judge said.

“I have concluded all the evidence that I have that the only proper sentence is one of detention for life.”

He said the boy would face life in jail with a minimum jail term set at five years with his final release to be determined.

Judge Saunders acknowledged some progress had been made in de-radicalizing the youth but significant risks remained.

He hoped setting a five year minimum term after which he hoped the risk would lessen and he could be released.

The youth, who cannot be named for legal reasons, now becomes the youngest person in Britain to be sentenced for a terrorist related offence.

Judge Saunders said the boy assisted in the planning the attack and ensured the person he was inciting stayed on track to carry out the plot on Anzac Day, chosen because of its national importance to the people of Australia.

He said that such an act by a boy of 14 who became so radicalized as an extremist he was driven to killing was “chilling”.

He described the boy’s role in the plot as a “vital part”, and said that his beliefs had become so deeply rooted one radicalizing expert had never seen such entrenched radical views in a suspect.

On Thursday, prosecutor Paul Greaney QC read out a 32-page sentencing brief outlining a plot by the youth to incite via 3000 online encrypted messages a Melbourne man (allegedly Sevdet Besim), 18, to carry out an atrocity during this year’s Melbourne ANZAC DAY parade.

That plot included decapitating a police officer, driving into a crowd with a car with an ISIS flag on the bonnet, shooting other police that would arrive on the scene and practicing decapitating a loner in the days leading up to the event.

The youth was also in direct contact with notorious Australian ISIS recruiter Khaled al-Cambodi as well as three terrorist-linked British hate preachers, who were recently killed in a drone striker ISIS fighter Abu Hussain al-Britani, a notorious Canadian terrorist, had incited a mother in America online to raise her children for suicide martyrdom, operated 89 Twitter accounts for expanded family of jihadists, had 23,000 Twitter followers and had a list of teachers he said he wanted to kill and decapitate.

In his defense, the court heard the boy had been seduced and radicalized by what he was reading online that filled a “void” in his personal life that involved a broken home and lack of role model or male mentors, a sense of isolation and marginalization. On social media however he was a “hero” to thousands of followers for his praise of jihad and love of ISIS and death.

He would go to school, be turned away because he would not hand his mobile phone over, then spend the rest of his day sitting by a dam communicating with jihadists across the world before going home and pretending he had been at school all day.

“The phone gives (name) his sense of identity … the way in which he talked was fantasy he was creating an image for himself far removed from reality … he was a celebrity within that Twitter jihadi community,” defense counsel James Pickup QC told the court. He said his client know new what he had done was “barbaric, immoral and wholly wrong” and he was rehabilitating.

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