Police investigating the murder of Jodie Chesney have been give more time to question an 18-year-old suspect.
The 17-year-old was fatally stabbed in a park in Romford, east London, on 1 March.
Manuel Petrovic, 20, of Highfield Road, Romford, and a 16-year-old who cannot be named are both due to face trial over her murder in September.
The 18-year-old was arrested on suspicion of murder on 10 March and remains in custody.
Metropolitan Police officers have been given a warrant for his further detention, which expires on Wednesday evening.
Another three people – a 50-year-old man and a 38-year-old woman, both from Dagenham, and a 17-year-old were arrested on suspicion of assisting an offender.
They have all been released under investigation.
Jodie was playing music with friends when was she was stabbed from behind.
A post-mortem gave her cause of her death as trauma and haemorrhage.