A fourth person has been charged with the murder of girl scout Jodie Chesney, who was stabbed to death on 1 March.
The 17-year-old boy was charged with murder and possession of a stun gun on Sunday, the Met Police said.
He is due before Barkingside Magistrates’ Court on Monday.
Three other people have been charged with Jodie’s murder: Manuel Petrovic, 20; Svenson Ong-a-kwie, 19; and a 16-year-old boy.
They are all from or around Romford, east London, and are due to stand trial on 2 September at the Old Bailey.
Jodie, 17, had been playing music with friends at Harold Hill, Romford, when she was stabbed from behind.
A post-mortem gave the cause of her death as trauma and haemorrhage.