Detectives investigating the murder of Jodie Chesney have been given more time to question a teenage suspect.
Jodie, 17, was knifed in the back near a playground in Harold Hill, Romford, on 1 March.
Two people, including a 16-year-old boy, have been charged with her murder.
An 18-year-old man was arrested on suspicion of murder on 10 March. Officers have secured a warrant for his further detention, which expires on Wednesday evening.
Manuel Petrovic, 20, of Romford, and the teenage boy, who cannot be named, are both due to face trial at the Old Bailey in September.
Another three people - a 50-year-old man and a 38-year-old woman, both from Dagenham, and a 17-year-old boy, all arrested on suspicion of assisting an offender have been released under investigation.
Jodie is the fifth teenager to be stabbed to death in the capital so far this year.
Her father Peter Chesney led tributes, describing his daughter, who was a keen scout, as a "great girl" and a "proud geek".
Jodie was pronounced dead after police were called to the park near St Neot's Road at 21:25 GMT on 1 March.
She was with friends at the time of the attack.
A post-mortem examination gave the cause of her death as trauma and haemorrhage.