A 14-year-old girl has been arrested on suspicion of the murder of a teenage boy in Brixton, south London, who was stabbed to death.
The 15-year-old victim was reportedly stabbed more than once during the incident on the Loughborough estate.
Police were holding the suspect at a south London police station, where she was being questioned in the presence of an adult.
Early enquiries suggested the boy was not a victim of gang-related dispute.
More arrests were expected to follow in what a Scotland Yard spokesman called a "fast moving enquiry."
The victim died after emergency crews spent a significant amount of time trying to resuscitate him in the street.
A Metroplitan Police spokesman said they knew the name of the boy but had not named him formally.
CI King said: "We would appeal for anyone who has any information or witnesses to come forward as soon as possible."