Detectives investigating the murder of a 16-year-old boy have made two further arrests.

Alex Smith was stabbed repeatedly in Munster Square, Camden, north-west London, on 12 August after being chased by a group of people.

A 19-year-old man was arrested at an address in Camden on Saturday on suspicion of murder and remains in custody, Scotland Yard said. Another 19-year-old man was arrested at an address in Wembley, north-west London, on Sunday on the same charge and is also in custody.

Smith, from Brent, north-west London, died from a stab wound to the chest, a postmortem examination found on Thursday.

A 23-year-old man and an 18-year-old man both arrested on suspicion of murder on Wednesday have been bailed until mid-September, according to the Metropolitan police. A 20-year-old man arrested on Friday on the same charge was also released on bail until mid-September.

A group of young men were heard “screaming and laughing” as they pursued Smith with a machete, according to witnesses.

Smith was heard shouting “help me” before collapsing near the doorstep of a family home, one witness said. The teenager died at the scene after police were called.