Police said on Thursday they had charged four teenagers, including a girl, with the murder of Shakilus Townsend, stabbed to death in south London last week.
Townsend, 16, was found with a stab wound in the entrance to a block of flats in Thornton Heath last Thursday. He died in hospital the following day.
Detectives have charged Tyrell Ellis, 18, two other young men aged 16 and 17, and a 15-year-old girl with murder. They are due to appear at Sutton Magistrates Court later on Thursday.
A 22-year-old man has been released on police bail until a date in August pending further investigations.
Police said they had arrested another suspect, a 16-year-old, and he was being quizzed at a police station in south London.
Townsend was one of 19 teenagers to die violently in the capital this year.
The Metropolitan Police have said knife crime was now the force's top issue.
Officers say they have searched 27,000 people, arrested more than 1,200 and seized 500 knives in London during a six-week crackdown. A 75-strong team has also been set up to target those carrying weapons.
"This reflects that tackling knife crime is the number one priority for the Met at this time," said Deputy Commissioner Paul Stephenson.
