A 16-year-old has been given a life sentence with a minimum term of 12 years for the murder of 14-year-old schoolboy Martin Dinnegan.

Martin was chased by a gang and stabbed in the back four times near his home in Holloway, north London, in June last year.

Joseph Chin will serve at least 12 years while Kevron Williams, 17, who was convicted of attempting to cause grievous bodily harm, was given four years in youth detention.

The court was told that Martin had been on a bus when looks were exchanged with a rival group on bicycles. Following another encounter when one of the rivals received a cut, Martin ran away and was chased along the street and stabbed.

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 then 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.

Aftab Jafferjee QC, prosecuting, said Martin 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.

Mr Jafferjee said teenagers showing off in front of their friends and being prepared to use violence is now a scourge of cities and towns.

He said: "This is such a case, which leads from dirty looks to death in one hour."

Judge Brian Barker, the Common Serjeant of London, said: "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."

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