A mother wept in court as one of the youngest children to plead guilty to murder was locked up at the UK's Old Bailey for a minimum of 11 years.
The 13-year-old boy, who cannot be named for legal reasons, pleaded guilty to stabbing 53-year-old Christopher Barry twice in the chest outside his home in Edmonton, north London, on December 14 last year.
Mr Barry - who was a builder, originally from Cobh Co Cork - was stabbed after he tried to stop a group of teenagers gaining entrance to his apartment building.
The court heard he had left a 13th birthday party with a group of friends to see another boy on to the bus home in time for an 8pm curfew.
But on their way back to the party, they went to the wrong block of flats and came across Mr Barry, accompanied by his girlfriend Sabrina Finn, outside.
When the victim refused to let them into the building, there was “pushing and shoving” between Mr Barry and the three boys before the defendant managed to get in.
He followed Mr Barry into the lift where he produced a kitchen knife from his rucksack and demanded “What you saying now? What you saying now?” before stabbing him twice.
Mr Barry did not know straightaway that he was hurt, and realised only when he took off his wax jacket inside his flat and noticed blood on his shirt, Zoe Johnson QC said.
Shortly afterwards, he collapsed in a pool of blood and went into cardiac arrest, she said. He died shortly afterwards.
Meanwhile, the boy had texted one friend “Ok, if anyone asks, I wasn’t there today”, and told another he was going to prison.
The court heard the boy had been a member of a Wood Green gang since he was just 10 and had been excluded from a school after receiving a police warning for carrying a knife on its premises.
The girlfriend of Mr Barry, who was known as Jack, attended today's sentencing by judge Stephen Kramer.
Ms Finn said in a victim impact statement: “I’m back at work now and although I walk, talk and look the same as I did before, inside I’m tired and my heart is broken.
“Jack and I had four happy years together and this young man has taken that away from me. 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.”
In mitigation, the boy’s lawyer Michael Turner QC said this was a “unique” case and in all his years as a barrister it was the only time such a young defendant had pleaded guilty to murder.
The boy’s mother wept in court as Judge Kramer sentenced her son to be detained at Her Majesty’s pleasure for at least 11 years.
The judge told him: “You are only 13 years old but shortly after 7.30pm on the evening of December 14 2014, you were carrying a knife in your bag.
“You wanted to get into a block of flats but you went to the wrong block with tragic consequences for everyone involved.”
He took into account the boy’s remorse, revealed in a letter from his mother which was not read out in court.
The letter also detailed a “troubled background as well as positive aspects”, the judge said.
Judge Kramer refused an application by the press to lift a legal ban on naming the boy, saying there were “exceptional” circumstances.