Three people have been arrested in connection with Alan Cartwright's murder, the Metropolitan police said on Wednesday.
The force said a 17-year-old male was arrested on suspicion of murder at a residential address in Camden and remains in custody.
An 18-year-old man was also arrested on suspicion of murder after attending a north London police station. He remains in custody.
A 21-year-old man was arrested in Camden and is in custody at a central London police station.
The Metropolitan police have released CCTV footage of the moment a 15-year-old boy was fatally stabbed while cycling in north London on Friday evening.
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Alan Cartwright and his two friends were attacked while riding along Caledonian Road, near the junction with Copenhagen Street, in Islington.
Cartwright was stabbed in the chest and managed to escape but collapsed a short distance away.
Emergency services attended the scene and the teenager was pronounced dead a short time later.
The CCTV footage released on Tuesday shows two suspects step off the pavement from the right-hand side of the road, with “suspect one” stabbing Cartwright in the chest and “suspect two” knocking one of his friends off his bike.
Detective chief inspector Chris Jones said: "The footage of the suspects attacking Alan and his friends is truly shocking."
Police have released these descriptions of the three suspects:
Suspect one is described as a male youth of slim build. He is believed to have been wearing a grey or dark-coloured hooded top and dark bottoms that could have had a keychain hanging from the rear pocket. He was wearing some sort of face covering but is thought to be white.
Suspect two is described as a male youth of slim to medium build. He was wearing a black sleeveless jacket with a black hooded top underneath. He was wearing a shoulder bag across his body. He too was wearing a face-covering but is thought to be black.
Suspect three is a male youth of medium build. He was wearing a three-quarter-length coat with a hood that appeared to have some sort of trim around it. He was also wearing a dark top with a multicoloured motif on the chest, lighter-coloured bottoms, and dark shoes. He too was covering his face. There is no information as to his ethnicity.