Three teenage boys were being questioned today on suspicion of murdering a 15-year-old aspiring rapper thought to have been killed while protecting his younger brother.
Negus McClean died from a stab wound to the heart on Sunday evening after being attacked in Edmonton, north London.
A 14-year-old, a 16-year-old and a 17-year-old were detained yesterday and were being held in police custody last night, Scotland Yard said.
It is believed that around 13 young black men, thought to have been on bicycles, chased Negus prior to the murder.
Two men aged 20 and 18 and two boys aged 16 and 14 have already been arrested over the killing and bailed pending further inquiries.
The 16-year-old is due to return to a north London police station on Monday and the other three were bailed to return to a north London police station on May 6.
Officers were called at 7.25pm on Sunday to Westminster Road, where local boy Negus had been stabbed in the chest and thigh.
The victim's cousin Noel, 25, said he died protecting his brother in a "selfless act".
Detective Chief Inspector Stephen Clayman said: "We continue to seek witnesses and those with information about who was responsible for this murder.
"It is vital that the public, and especially young people, have the trust and confidence to speak to the police in these situations."
* Anyone with information is asked to call police on 020 8345 3775 or Crimestoppers anonymously on 0800 555 111.