Joshua Williams (pictured) stabbed Alan Cartwright in the chest as he cycled along a busy street in Islington, North London, with friends.

The grieving family of a popular 15-year-old murdered in a horrific street stabbing have described him as 'amazing' and 'the best'.

Joshua Williams, 18, stabbed Alan Cartwright in the chest in an 'utterly senseless' attack as he cycled along a busy street in Islington, North London, with friends.

College student Alan was at the head of a group of four youngsters when they were set upon by three robbers.

Williams was today found guilty of killing the bike enthusiast by plunging a blade deep into his chest as he cycled by, a charge he denied.

Speaking after the trial concluded this afternoon, tragic Alan's heartbroken parents Alan Cartwright and Michelle Watson, and older sister Cherrie Ives, paid tribute to the much-loved teen.

Ms Watson, who is a bus driver, said: 'Alan was just a normal 15-year-old boy - loved his bikes, his family, being out with his friends. He was just a funny little kid, at the end of the day.'

His sister added: 'His friends have always said he never liked confrontation and was always polite - just a happy person.

'He was amazing, honestly. I know everybody says about their little brothers they're little rats.

'We wouldn't change him for the world. The best brother.'

Alan, who they described as a 'cheeky' joker who also had passions for music and go-karting, had been on his way to a monthly Critical Mass cycling event with his friends when he was set upon by Williams in February of this year.

The 18-year-old was part of a group of robbers who deployed a ruthlessly effective 'pincer movement', which helped them steal the bikes of two of Alan's friends in an attack that was described as 'brazen and swiftly executed'.

CCTV footage of the scene showed how Alan, known to his family as 'Little Al', made a desperate attempt to escape on his bike after the knife punctured his lung but collapsed a few yards up the road.

'Utterly senseless' attack: College student Alan Cartwright, pictured, was at the head of a group of four youngsters who were cycling along a busy road when they were set upon by three robbers

Paramedics rushed to his aid but could not save him. He was pronounced dead less than an hour later on the street in Islington, North London.

Five days later Williams was taken to Islington police station by his parents, who told an officer that their son was responsible for the boy's murder.

At the time of the attack, Williams had been on police bail on suspicion of possessing a four-inch lock knife although he was never charged.

Williams claimed to have an alibi but now faces a life sentence after he was convicted of murder and conspiracy to rob following a trial at the Old Bailey.

On the evening of February 27, Alan was cycling with friends when Williams and two other youths intercepted them in front of motorists and pedestrians, the court heard.

In just seven seconds, they stepped out in front of the cyclists and took two bikes before Williams approached Alan in the road and swung a knife at his chest in a 'deliberate and gratuitous' stabbing.

Joshua Williams was captured on CCTV stabbing Alan Cartwright in the chest as he cycled along a busy street in Islington, North London, with friends. Williams was today found guilty of murder at the Old Bailey

As his two friends were robbed of their bikes, a mortally-wounded Alan managed to cycle on before collapsing a short distance up the road. Bystanders rushed to help before paramedics arrived.

Meanwhile, Williams hopped on the back of one of the two stolen bikes, leaving Alan for dead.

Shaquille Roberts, 19, and a teenager who cannot be named for legal reasons, have since pleaded guilty to the robbery.

Malcolm McHaffie, CPS London Deputy Chief Crown Prosecutor, made clear that the 'horrifying' stabbing was a planned act of 'devastating' violence.

In just seven seconds, they stepped out in front of the cyclists and took two bikes before Williams approached Alan in the road and swung a knife at his chest in a 'deliberate and gratuitous' stabbing

He said: 'This was a completely unprovoked attack on a young teenager who was spending time having fun with his friends.

'The three defendants had clearly made a plan to rob the group of friends of their bicycles, however, Williams decided to take this further and use a knife in a deliberate attack on one of the cyclists, with catastrophic consequences.

'This case shows the horrifying results of knife crime and how a life can be lost and a family devastated in a matter of seconds.

'CPS London is committed to tackling knife and gang crime in the capital and we will continue to work with our criminal justice partners to robustly prosecute offenders.

'I would like to express our sincere condolences to Alan's family, our thoughts are with them at this time.'

In the days that followed the attack, Alan's parents made emotional public appeals for witnesses. They described a teen who 'always made you laugh' and was a member of the cadets.

On March 4, Williams went to Islington police station with his parents to hand himself in, the prosecution said.

When asked why they were there, his mother told an officer it was about the incident in Caledonian Road, saying: 'Yes, he's involved, he did it.'

And as he was taken into custody, Williams, was heard by another officer to say: 'It's the right thing to do, isn't it?'.

But in his defence, Williams claimed he was at a youth club that night and he only went to the police station to tell them that he was not involved in the incident.

The court heard that the defendant, nicknamed Slimzy, was identified as the third robber in a comment about the CCTV footage which was released by police and posted on YouTube.

Alan, circled left, was captured on CCTV cycling towards Williams, right, who was seen hiding behind a car

Two members of gang were seen on camera attacking Alan's friends. Alan remains unaware of the man approaching him from his left

His parents and brother also gave evidence to back up his claims, however the jury had spotted the apparently religious family did not all swear on the Bible in the witness box.

Prosecutor Jonathan Rees QC told jurors the evidence from his family was 'disappointing' because they had 'decided to abandon their principles to support him in his lies to the court'.

He suggested the defendant carried a knife on the day of the robbery because he was the victim of an earlier knife attack at the hands of a group of youths.

The prosecutor also pointed out that the CCTV showed the killer who wielded the knife was clearly left-handed - the same as Williams.

Williams then leaps out from behind the car with his arm extended, brandishing the knife as Alan passes

Alan is stabbed once in the chest during the attack, which the Old Bailey heard lasted just seven seconds

The jury took three hours to reject Williams' explanation. Williams, of Upper Holloway, north London, denied murder and conspiracy to rob.

He will be sentenced alongside 18-year-old Shaquille Roberts and a 16-year-old who have already pleaded guilty to the bicycle robbery.

Alan's mother Michelle Watson, 40, who has her son's face tattooed on her arm, sobbed as the verdicts were announced.

She and Ms Ives held hands with Alan senior as their eyes welled up with tears as a victim impact was read out.

Following today's verdict, they called for more stop and searches and tougher 10-year mandatory sentences for possessing knives to deter young people.

His father Alan Cartwright senior, 44, said: 'It will make people think twice about carrying a knife.'