Metropolitan Police Service
Attack was not terror related, says Scotland Yard.
Another teenager received multiple stab wounds in the south east of the capital.
Estonian national Kirill Belorusov was brought back to the UK.
He is in a life-threatening condition.
Road closures are currently in place.
Police release CCTV footage as victim remains in critical condition a week after attack.
She was found in a shallow grave after going missing.
The teenager was arrested on Friday.
Armed police arrested two men, aged 50 and 77, following the discovery.