A 16-year-old boy stabbed a younger teenager to death in the street while under a supervision order for kicking a shopkeeper unconscious. Joseph Chin stabbed 14-year-old Martin Dinnegan four times in the back after a chase near his home in Holloway, north London, in June last year.
Yesterday, as Chin was sentenced to a minimum term of 12 years in prison, it emerged that he had a criminal record dating back to 2004, including the possession of a snooker ball in a sock and threatening a man with a hollow bar.
In September 2006, he was given a 12-month supervision order after kicking a shopkeeper unconscious when challenged for stealing some food from outside the shop, and was still subject to the order when Martin died the following June.
Judge Brian Barker said: "This was a deliberate attack requiring a long chase with revenge in mind.
"It was an attack carried out without any regard to the standards and rules that we live by and no thought for the victim, his friends and his family."
He added: "The public have every right to be concerned about the increase growth of this sort of violence.
"It is a tragedy that this sort of triviality caused such a young man to lose his life and has caused enduring heartache to his friends and family."
In a victim impact statement, Martin's mother, Lorraine Dinnegan, said: "Martin was a charming, loving boy who has left us with cherished memories that will remain with us for ever.
"The pain that Martin's death has caused for our family is indescribable. Life will never be the same, a piece of our heart has been taken.
"We as a family will never make sense of the unnecessary suffering that was inflicted upon Martin. It was extremely sad to be burying Martin at the tender age of 14."
She said four days before he was killed, Martin had written a piece of religious education homework on the subject of a parable in which a man was chased by a group and left for dead by the side of the road.
Mrs Dinnegan's statement was read out in court by her eldest son, James, while Jim, her husband of 17 years, sat beside her. Martin was the second of their five children.
The trial was told that Martin had been on a bus when looks were exchanged with a rival group on bicycles.
Following another encounter in which Chin received two cuts, Martin ran away and was chased along the street. He was caught by Kevron Williams, 17, who punched him to the ground and stabbed him in the buttocks with a screwdriver, but Martin got up and continued to flee.
Tom Morgan, a witness who lived in the area, said he saw Martin running past him pleading: "Please help me."
He saw a "white-faced" and "very scared" Martin raise his hands as if to placate a youth who approached him on a BMX bicycle. But the cyclist, Chin, knocked him to the ground and pinned him down.
"Then I saw what seemed to be a stabbing motion, rather than a punching motion four or five times in very rapid succession," said Mr Morgan.
Martin, a pupil at St Aloysius College in Archway, lived on a local housing estate where there was rivalry with youths living on another estate.
Mr Jafferjee said he was "entirely without blame during the final confrontation" and had, in fact, fled from the encounter.
"Martin probably did not know when he began running away that he was running for his life – pursued for such a distance by these defendants on cycles and mopeds," he said.
Kevron Williams, who was convicted of attempting to cause grievous bodily harm, was sentenced to four years' detention.
Aftab Jafferjee QC, for the prosecution, said teenagers showing off in front of their friends and being prepared to use violence was now a scourge of cities and towns. "This is such a case, which leads from dirty looks to death in one hour."
Acting Detective Chief Inspector Stewart Hill said: "This is a tragic case and the impact on Martin's family and friends cannot be quantified.
"The murder of Martin highlights the potential fatal consequences that may result from carrying knives and other weapons. In this case an innocuous meeting of two groups of youths escalated in to a series of confrontations resulting in Martin's tragic murder.
"The investigation into Martin's murder has established that any of those youths involved in these confrontations could just have likely become the victim in this case.
"Our hearts go out to the Dinnegan family for their tragic loss."