Martin was stabbed four times in the back
A 16-year-old youth has been given a life sentence for stabbing to death a schoolboy who gave him a "dirty look".
Martin Dinnegan, 14, was chased and stabbed near his home in Holloway, north London, in June 2007 after exchanging "dirty looks" with a gang.
Joseph Chin was convicted of murder at the Old Bailey last month. He has been ordered to serve a minimum of 12 years.
Kevron Williams, 17, was sentenced to four years for attempting to cause grievous bodily harm during the attack.
Judge Brian Barker said: "The public have every right to be concerned about the 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 (it) has caused enduring heartache to his friends and family."
Outside court Martin's mother Lorraine said: "The pain that Martin's death has caused for our family is indescribable.
"We as a family will never make sense of the unnecessary suffering that was inflicted upon Martin."
She added: "Life will never be the same, a piece of our heart has been taken."
The court heard that the row began when a group on a bus and another group on bikes gave each other "dirty looks".
Joseph Chin (left) and Kevron Williams were both jailed over the stabbing
The youths on cycles then followed the group from the bus.
The groups clashed twice - first in a nearby park then an hour and a half later next to a housing estate.
In the second confrontation, Martin and another youth clashed with Chin, who was left with a cut on his shoulder.
Martin then fled, chased by members of the rival group.
He fell to the ground and was stabbed four times in the back by Chin.
The judge told him: "This was a vengeful attack out of all proportion to what may have gone before and no mercy was shown."
He said Williams had led the hunt for Martin out of a "determination to be involved" in the violence.
During the trial prosecutor Aftab Jafferjee QC said that 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," Mr Jafferjee said.
Mrs Dinnegan said she was "pleased" with the sentences.
"We are just hoping that the people who have been involved with Martin's murder will learn from what has happened to Martin," she added.
"We hope they come out of it better people."