Two teenagers and a 21-year-old were today arrested on suspicion of murdering a 15-year-old boy stabbed to death during a botched bicycle theft.

Alan Cartwright was attacked as he rode along the Caledonian Road in Islington, north London with friends on Friday night.

After a police appeal, which included CCTV footage of the moment he was stabbed, two teenagers were arrested on suspicion of murder by Scotland Yard detectives.

An 18-year-old man walked into a north London police station and a 17-year-old boy and a 21-year-old were held at in Camden this morning. All three are in custody.

It came after Alan's mother Michelle yesterday made an emotional appeal for information about her son's death.

This is the moment when Alan Cartwright was stabbed on his bicycle as he cycled through north London

This is the jacket Alan Cartwright wore when he was stabbed as he rode along the in Islington, north London

Alan Cartwright, pictured, suffered single stab wound to the chest when he was attacked on Friday night while he cycled along a busy London street when he and his friends were attacked by a gang

Alan's mother Michelle Watson, left and his sister Cherrie Smith, right, appealed for witnesses to speak out

Alan’s mother and sister described the Army cadet and Celtic and Arsenal fan as a 'joker' who loved bikes and never caused any trouble.

Fighting back tears, Alan’s mother Michelle Watson, 39, said: 'He always made you laugh about anything and everything. He was just the funny one out of his friends.

'I feel angry, I want somebody found for this. I just feel numb.

'Looking at the CCTV footage it looks like he got punched, like somebody had just hit him.

'It was so quick, he just carried on riding and two minutes up the road he is collapsed and dead. It’s like it’s not real.

'I would say to witnesses, if you’ve got any sort of conscience come forward because a brother and son is dead.”

The teenager’s sister, Cherrie Smith, 21, broke down when she spoke of him not being there when she gets married.

Ms Smith said that her brother’s death has not fully sunken in yet because the family have not seen his body.

The teenager (left) pictured with his sister Cherrie Smith, 21, (right) who said his death had not sunk in yet

Alan Cartwright, pictured, was stabbed as he cycled along Caledonian Road on Friday and died in hospital

The teenager is described as a someone who 'wouldn't hurt a fly' and well-known in the area in north London

Alan with his older sister Cherrie, who appealed to the public today along with her mother in an emotional bid for his killer to be found

She said: 'We want any witnesses to give as much information as they possibly can. If you have a little brother or sister, ask yourself "what if it was them?"

'If that was me, I wouldn’t be able to live with myself.

'People are saying "wrong place, wrong time", but those people shouldn’t be carrying knives on them. The whole of his life Alan has grown up in the Cally (Caledonian Road) and you just don’t expect it.

'He has always put a front on in front of me and his friends that he was like a hard man, but he wouldn’t hurt a fly, he really wouldn’t.

'I just clearly hope someone gets found for this - knowing he has been taken away from us in such an unlawful way, it’s just heartbreaking because there’s a chance someone could get away with this.

I would say to witnesses, if you’ve got any sort of conscience come forward because a brother and son is dead Victim's mother Michelle Watson

'We clearly think it was a bike robbery, but the question is "why"? Why has that person done that?'

Yesterday police released shocking CCTV footage showing the moment the Holloway School student was stabbed.

The footage captures how he is struck in the chest as three partially masked youths leap out from behind parked cars on a busy road.

The schoolboy manages to cycle on only to collapse moments later and die from a single stab wound to his heart.

Meanwhile the robbers calmly push his friends from their bicycles and ride off as commuters and shoppers pass by oblivious to the unfolding tragedy.

Alan, a pupil at Holloway High School, can be seen in the images wearing a blue body warmer and grey jumper at the front of his group of friends.

As he passes a parked car a man darts out from his ‘blind spot’ and lashes out towards his chest. A second youth knocks one of Alan’s friends off his bike and a third attacker, wearing a hoodie, drags another to the ground. The killer, wearing a dark hooded top and with a keychain hanging from his back pocket, watches before getting on the back of one of the stolen bikes.

Despite the blood pouring from his chest, Alan managed to cycle a short distance before collapsing in the street.

A post-mortem examination on Monday concluded that the cause of the Holloway School student's death was a single stab wound to the chest.

Ms Watson, pictured, said witnesses with 'any sort of a conscience' should come forward with information

Ms Watson, left, comforted her daughter Cherrie, right, during the highly emotional press conference

Cherie Smith, left, and Michelle Watson, right, spoke of their horror after hearing about Alan's murder

Detective Chief Inspector Chris Jones, who is leading the investigation for the Homicide and Major Crime Command, appealed for help in identifying the three suspects.

'The footage of the suspects attacking Alan and his friends is truly shocking. Alan stood no chance of defending himself against his attacker, who casually stepped out in front of him and stabbed him in the chest.

'It is obvious from the footage that Caledonian Road is busy with cars and pedestrians. We have already spoken to a number of witnesses who have provided helpful information to the investigation; however, I would like to re-appeal to anyone who may know something about Alan's murder and the robbery of the bikes.

'Where are the two bicycles that were taken? Someone may have noticed a new bike brought home or perhaps you have been offered a similar bike for sale? If so, I would urge you to contact the police.

Mr Cartwright's sister Cherrie Smith, right, said she cannot believe that he will not be at her wedding

'I would like to reassure anyone who is worried about contacting the police that they will be treated with the utmost sensitivity.'

Alan's mother, Michelle Watson, 39, from Islington, north London, led an emotional tribute to her son on Facebook. She wrote: 'Our baby boy xxxxxxx xxxxxxx x xxxxxxx RIP we love you always.'

Biddy O’Connor, 17, said: ‘Alan was an innocent young boy, he didn’t deserve what happened to him. Too many young people are dying. These people are carrying knives because they think they are brave or it makes them bigger. They are idiots. I don’t think young people appreciate the value of life enough.’

Detectives believe those responsible are members of one of the many gangs which torment residents of nearby estates.

The bicycles stolen during the stabbing were a red mountain bike and a black and red pedal cycle.

Mr Cartwright was stabbed as he cycled along the Caledonian Road on Friday at around 19.34.

He collapsed and later died at the scene, as three of the thugs escaped on two stolen bikes.

DCI Jones continued: 'I think the CCTV speaks for itself.

'I think this is a dreadful, shocking, unprovoked incident. It is a shocking crime, a mindless act of violence.

'One of the motives we are exploring is of robbery of the push bikes. I'm open minded to the motives however.'

Alan, circled left, is seen on CCTV approaching his attacker, circled right, who is hiding behind a car

Several members of the gang attack Alan's friends, who is unaware of the man approaching from his left

The attacker leaps out from behind the car with his arm extended brandishing the knife as Alan passed

He added: 'Alan is well known in that area.

'He was just out cycling in the area with his friends. Alan is just a young boy, 15 years of age. I don't class him as a gang member.

'He was just out cycling in and around the Caledonian Road area.'

He went on to say: 'A really important line of inquiry for us is where the bikes have gone. Has someone been offered them for sale, has someone purchased them?

'We have made an appeal for witnesses. I would really ask people if they saw anything on that night please come forward.

'I'm convinced that if you know these suspects you will recognise them, even from their clothes or build.'

Asked if the police have any possible suspects he said: 'I wouldn't discuss that at this time.'

One of the stolen bikes as a 'Specialized Hard Rock' mountain bike with disc brakes and electrical tape on the frame.

The second bike was described as a black and red 'specialized Vita' pedal cycle. The word 'Specialized' was printed in white.

Police believe the distinctive stolen bicycles could lead them to the killers. They asked residents to watch out for bicycles being offered for sale in suspicious circumstances.

The attacker stabs Alan once in the chest in an effort to steal his bicycle, leaving him with grave injuries

Alan manages to continue along the Caledonian Road mortally wounded as the gang attacks his friends

Police are appealing for witnesses following Friday's terrifying attack in north London

Mr Cartwright was declared dead at the scene on the Caledonian Road in North London on Friday

According to police, the first suspect is a male youth of slim build. He was wearing a grey or dark coloured hooded top and dark bottoms. He may have had a key chain hanging from the rear pocket. He is believed to be white.

The second suspect is also a male youth of slim to medium build wearing what is thought to be a black, sleeveless top. He was wearing a shoulder bag against his body. Eyewintesses said he had some form of face covering and is thought to be black.

The third suspect is a male youth of medium build and was wearing a three-quarter length coat. He was wearing a dark top with a multi-coloured motif with lighter coloured bottoms and dark shoes. Officers do not know this suspect's ethnicity.

Anyone with information on any of the suspects is asked to call the incident room on 020 8345 3734, or Crimestoppers on 0800 555 111 or via crimestoppers-uk.org.

Mr Cartwright's family released a video of the 15-year-old victim, who was described as a passionate cyclist