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Killed: Martin Dinnegan, 14, was stabbed after getting off a bus last June

A 16-year-old boy has been found guilty of murdering London teenager Martin Dinnegan.

Dinnegan, 14, was chased by a gang of youths and stabbed to death near his home in Holloway, North London in June 2007.

The 16-year-old boy from Finsbury Park, who cannot be named for legal reasons, denied murder, but was found guilty after only five hours of consideration by the jury.

A 17-year-old was found guilty of attempting to cause grievous bodily harm. He was cleared of murder and manslaughter.

Rene John-Baptiste, 21, of Plaistow, East London, and Sean Clark, 19, of Holloway, were cleared of all charges.

Dinnegan's distraught mother Lorraine cried out 'spit on them' at the three cleared of murder as she watched them embrace in the dock.

The 16-year-old and 17-year-old will be remanded in custody until sentencing on August 8.

During the trial at the Old Bailey, witness Tom Morgan told the court how Dinnegan ran past him pleading: 'Please help me.'

Mr Morgan said he saw the petrified boy hold his hands out in an attempt to placate one of his pursuers but Martin was felled by a punch to the head.

His attacker then pinned him to the ground and made repeated stabbing motions towards his back, the court heard.

Mr Morgan and his girlfriend rang 999 and, in a tape recording played to the jury, told the operator: 'There is a white guy and a massive group of black guys who are kicking the crap out of him.'

Aftab Jafferjee QC, prosecuting, told the jury how Martin was beaten to the ground and stabbed 'in a case that moved from dirty looks to death within an hour'.

Mr Morgan gave evidence today from behind screens to shield his face from the dock and the public gallery.

He told how he and his girlfriend had been on their way to get a DVD from a rental store when the boy he later recognised as Martin, wearing a grey tracksuit and hood, ran towards them.

'He was very white faced, he was sprinting towards us and shouted: "Help me, please help me,"' Mr Morgan said.

'He ran past us on the road to my left then a guy with a black tracksuit went past on a large-framed BMX.

Grief: James and Lorraine Dinnegan with a picture of their son Martin

'He was cycling after the victim and was the distance of one parked car away from us.

'He was very dark skinned although I was unable to see his face as he was wearing a black hooded jumper with the hood pulled up.

'He dropped the bike when he got alongside the victim. Martin stood still and put his hands up as if to placate the cyclist. Martin appeared scared, very scared.

'The effect on the cyclist was almost nothing whatsoever and the next thing was that a large haymaker came from his right fist. It was a right hook and the blow connected with Martin's head or neck.'

At this point Mr Morgan's attention was distracted by another youth sprinting up and shouting, the court heard.

'I looked back up the road and Martin was on the floor now,' Mr Morgan said.

'It looked as if the first assailant was leaning on top of Martin who was on his back and side facing away from us.

'The first assailant was leaning with all his weight on Martin's shoulder and upper arm pressing him to the floor so that Martin seemed to be pinned to the floor.

Crime scene: Police investigate on the night of the attack

'Then I saw what seemed to be a stabbing motion rather than a punching motion four or five times in very rapid succession.'

Mr Morgan explained that he had not seen a knife but, as he was experienced in martial arts and disarming those armed with knives, he could identify the difference between a punching and stabbing action, which he demonstrated to the jury.

He then told how a crowd of up to 20 people aged 'between 10 and 20' started 'laying into' Martin.

Mr Morgan rang 999 at 8.38pm, telling the operator that it looked as though one of the attackers had a knife.

Martin, a pupil at St Aloysius College in Archway, died at the scene.