A former gang member said he unknowingly stabbed a Mitcham teenager to death in front of terrified Boxing day shoppers because he was in fear for his life, a court heard.

Seydou Diarrassouba, 18, from Phipps Bridge, bled to death outside Foot Locker in London’s Oxford Street after he was stabbed twice in the chest on December 26, 2011.

The teenager had been stabbed through the heart with such force that the blade had broken off from its handle.

But his accused murderer, 23-year-old Jermaine Joseph, said he acted in self-defence after he was chased into the sportwear shop by Diarrassouba – known to his peers as ‘Nuts’.

The two were well-known to each because Mr Joseph was a former gang member who used to live in Mitcham until he was rehoused in Tottenham by Haringey Council in April 2011.

Appearing in court on Friday, November 9, Mr Joseph said he was receiving death threats from former gang members and – just weeks before the Diarrassouba’s murder - had told the council he received an anonymous phone call which said: “We know where you live and we’re coming for you.”

He said this prompted him to take a knife with him to ward off potential attackers when he went out in public, including on Boxing day when he went out to central London to spend his Christmas gift money.

He said: “I decided to take the knife out with me. I was afraid of being attacked in central London by black people, especially Nuts and his gang.”

After arriving in central London with 20-year-old Thulani Khumalo – who is also on trial for the murder – Mr Joseph said he was spotted by Diarrassouba in Oxford Street.

He said: “He looked at me and stopped walking. He started congregating towards his friends and walked towards me.... My first intention was to get to safety. I ran into Foot Locker. I thought if I run into the shop the CCTV and security guards would stop them trying to stab me.”

Diarrassoubba’s friends were named in court as Felix “Stagger” Ankah, of Lewis Road, Mitcham, Luis “Souza” Santos and Brian “Clips” Mudziwepasi.

Mudziwepasi was himself was jailed for 11 years this week for firing a gun at police officers in Morden Road, Mitcham, in February (two months after Seydou’s murder).

Mr Diarrassouba, a former business student at South Thames College and Rutlish School in Merton Park, was a member of the All About Money gang that had become suspected of robbery, violence and of having access to weapons.

Mr Joseph explained how the knife was in his pocket the whole time and was brandished when Seydou followed him into the shop and brandished his own knife.

He said: “As I ran into the shop I got near the tables and I felt like I ran into a wall of people. I turned around and I heard Seydou say to me: ‘Where you going?’

“He was running toward me. I could see he had a knife in his hand. It was in his right hand. I took out my knife and held it in front of me. I thought if I hold it out it will deter him from attacking me.

“He saw me reach for it and I took out the blade. He looked at the blade but carried on charge towards me. He swung his right hand, the hand that had the knife in it. I blocked his arm with my left hand.

The court was then told how Mr Joseph had stabbed Seydou in his left hipbone, but in the heat of the moment he was not aware Seydou had been stabbed at all.

Then, he said: “I started stumbling back and the crowd started to separate. As I was falling I swung at Seydou with my knife, I remember doing that.... I thought I stabbed him in the back.

He added: “As I swung my knife I heard the knife break. I wasn’t sure I even stabbed him. I thought it caught on to his coat and then it broke.

“I remember hitting the ground and I thought I was going to get stabbed. I curled up into a ball. I started feeling punches and kicks. Seydou was kicking me.”

During this time, there was a fist fight between the two groups of boys until Mudziwepasi and Mr Ankah left.

Mr Joseph said: “I looked to see if they were coming back. I could see Clips and Stagger running towards the shop. They were shouting something. I stepped back towards the escalator.

"They moved towards the front of the shop and said 'You stabbed him, you stabbed him. I’m coming round to your mum’s house. You’re dead. I know where you live.' It was Stagger, Felix, that was saying that. He said 'wallahi' which means 'I swear to God.'

Staff then brought down the front shutter of the shop as customers fled in terror. The Mitcham teens were stopped from coming back into the shop and Mr Joseph’s group were told to go upstairs for their own safety.

Mr Joseph denied he had any knowledge that he had stabbed Diarrassouba twice in the chest – causing him to stumble out into the pavement where he soon bled to death.

The trial continues.