Two boys have been arrested on suspicion of the murder of a 15-year-old who was killed while "selflessly protecting" his younger brother.
A 14-year-old and a 16-year-old were arrested and remain in police custody.
Negus McClean died from a stab wound to the heart on Sunday evening after being attacked in Edmonton, north London.
It is believed that around 13 young black men, thought to have been on bicycles, chased Negus prior to the murder.
Four males aged between 14 and 20 have already been arrested over the murder and bailed pending further inquiries.
Police arrested two men, aged 20 and 18, and two boys, aged 16 and 14, on Monday in connection with Negus's murder.
The 16-year-old was bailed on Tuesday to return to a north London police station on Monday and the other three were bailed on Wednesday to return to a north London police station on May 6.
Officers were called at 7.25pm on Sunday to Westminster Road, N9, where Negus, from Edmonton, had suffered stab wounds to the chest and thigh. The aspiring rapper would have celebrated his 16th birthday later this month.
His younger brother, who is believed to have recently started secondary school, witnessed Negus collapsing after the attack, locals claimed. Negus'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. We will deal with you and your information responsibly and there are many things we can do to make this process easier - please do not hold back information, you may be shielding those involved."