Jack Woodley was stabbed in the back after a night out at the fair in Houghton-le-Spring last October.
He died in hospital the next night.
Ten men, aged between 14 and 18, were convicted in June after a trial at Newcastle Crown Court in which witnesses described how Jack was “isolated” from a mob who were “like zombies attacking an animal”.
The 15-year-old who admitted causing the fatal stab wound was jailed for life with a minimum of 17 years. He pleaded guilty to manslaughter before the trial began, but the jury found him guilty of murder.
Judge Rodney Jameson told him: “The fact that you had a knife was no secret. You knew Jack was unarmed.
“Instead, knowing he was unarmed and not looking for trouble, you decided to use force.
“You stabbed once in the right hip. You had a chance to retire. Instead, you chose the moment to attack again and fatally stabbed him in the back.
“You’re getting a sentence longer than you’ve been alive. You’ll be 32 years old by the time you’re eligible for parole.”
Jack Woodley was stabbed with a 25cm long knife. Credit: CPS
The youngest defendant, who is 14, was given a minimum sentence of eight years.
Judge Jameson said he had been described by a psychologist as a “vulnerable young boy”.
The judge said he essentially had a learning disability and this reduced his ability.
He told him: “What you did was bad. You are not as guilty as most of the others in the dock. You may find it harder to face custody.”
He will be eligible for parole when he is 22.
The other eight defendants were sentenced to between eight and 15 years in prison.
The attack took place near the Britannia Inn. Credit: ITV Tyne Tees
During the trial, cellphone footage was played showing the teenagers closing in on and surrounding Jack. Someone is heard shouting “get the helicopter out”.
The group punched, kicked and stamped on Jack during the attack. Witnesses described it as “animals attacking prey”.
Prior to the sentencing, nine of the defendants launched a bid to have their convictions overturned.
A spokesman for the Crown Prosecution Service (CPS) said: “We can confirm that we have now received notices of appeal against conviction from nine of the 10 defendants found guilty in this case.”
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