The teen – who cannot be named for legal reasons – was a member of the notorious Wood Green Gang in London.
The Old Bailey heard how he pulled a knife from his backpack and stabbed Christopher, a builder, who had refused to let them back into a block of flats to return to a 13th birthday party on 14 December 2014.He stabbed Christopher twice before fleeing the scene.
In text messages later that evening, he had told a friend, “I’m going to prison” before writing on Facebook: “The thing I'm going to miss most when I go pen [penitentiary] is NY gyal [New York Girl].”
The boy is one of Britain’s youngest ever murderers.
During the court case, the jury heard how the boy was expelled at 11 for carrying a knife.
Judge Stephen Kramer QC said: “When Mr Barry returned home, he refused to let you in to that block but you nevertheless got in. You followed Mr Barry, produced your knife, and then stabbed him twice in the chest.
“The injury to the chest went through clothing including a wax jacket and went deep.”
Now behind bars, the boy has deemed a high risk of causing harm.
Christopher’s girlfriend, Sabrina Finn, who was with him at the time said in a victim impact statement that her heart was broken.
She said: “Jack saved my life last year when I had a serious medical condition which required emergency surgery. I could not do the same for him. Due to the nature of Jack's death I had to leave my home. It was a home that Jack and I put a lot of time and money into for the future we thought we would have together.”