A 15-year-old boy who stabbed a market trader to death in a "primeval split-second of anger" was ordered today to spend at least 15 years behind bars.

Rashid Naeem, 29, was attacked near his stall in Queen's Market in Green Street, east London, in a row over a stolen watch in front of terrified families and children.

Following an Old Bailey trial, Karlton Burton, 15, was found guilty of the murder in February and detained for life in a young offenders institute.

Judge Richard Hone QC told him: "By your actions that Sunday you have, in effect, passed a life sentence on all the members of your victim's close family.

"Rashid Naeem has two young children who will never again see their father. The pain and devastation you have caused to these innocent people is beyond description.

"You killed a totally innocent family man with a knife. In that primeval split-second of anger and stabbing there is probably no distinction between an intention to really seriously injure with a knife and an intention to kill."

Javauntee Campbell, 17, who landed a punch on the victim, was convicted of manslaughter and detained for 10 years. A third defendant, aged 15, was cleared.

Burton had been diagnosed with attention deficit hyperactivity disorder and had the maturity of an 11-year-old boy, the court heard.

And at the time of the killing, when he was just 14 years old, he was on bail for taking an axe to a car in January this year.

The judge told him: "At your best, you can be well behaved and pleasant but there is a really bad streak in your character that means you over-react to perceived insults."

Sentencing Campbell, Judge Hone said that while he came from a supportive family and was of previous good character, it should not be forgotten that an innocent man lost his life in what was usually a peaceful Sunday market full of families and children.

During the trial, the court heard how Mr Naeem and his brother were working on the stall that sells mobile phones and watches on the afternoon of Sunday, February 16.

At around 2.40pm, the three boys went to the stall and "started fiddling around with some of the objects", prosecutor Sean Larkin QC said.

Campbell, then 16, took a watch from the stall and they walked off, before returning within a few minutes to a neighbouring stall.

Footage caught on CCTV showed that as the two brothers approached the defendants, Burton reached down to his ankle and got out a knife from his sock, concealing it in his jacket.

He said: "The two brothers are unarmed and they go over and ask for the watch back and there is a struggle, in the course of which ... the deceased is stabbed in the chest."

The three defendants ran away but were spotted nearby around an hour later by emergency services attending the incident. The murder weapon has never been recovered.

Later, the boys met up again at Campbell's house where the 16-year-old said he confronted Burton about what had happened.

While giving evidence in his defence, Campbell said: "I asked him 'did you poke the guy?' He said 'no I don't think so, it did not go in'."

He said he became "angry", adding: "I called him stupid and I told him why. I was shocked."

Burton did not dispute being responsible for stabbing Mr Naeem but said he acted in lawful self-defence, a claim which was rejected by the jury.

The prosecution said the defendants, from east London, were all part of a joint enterprise and the other two provided strength in numbers. The jury convicted Burton of murder, Campbell of manslaughter and cleared the third boy.

Members of Mr Naeem's family sat in the courtroom as the two boys were sent down.

Later, investigating officer Detective Inspector Ken Hughes said: "Rashid Naeem was killed as he tried to protect the business he ran with his brother.

"This was a cold-blooded killing in broad daylight, carried out in a merciless fashion.

"Burton and Campbell attended the market armed with a knife. Whatever their intentions, to come armed meant they were prepared for violence.

"Throughout this trial, the defendants showed no remorse, despite having ample opportunity to do so. I can only hope that today's sentencing give Mr Naeem's family some form of closure."