A 16-year-old girl has been arrested on suspicion of murder after a 22-year-old man suffered multiple stab wounds in south London.
Two men, aged 19 and 21, had earlier been held over the death of Ayodeji Habeeb Azeez on a street in Anerley on Sunday.
The pair were released under investigation.
The Metropolitan Police said Mr Azeez, from Dagenham in east London, was killed in the "middle of the day" in what "would normally have been a quiet environment".
The force said in a statement: "A 16-year-old girl was arrested this morning Friday 9 November at an address in south London on suspicion of murder.
"A post-mortem examination which took place at Princess Royal Hospital Mortuary on Tuesday, 6 November gave his cause of death as multiple stab wounds."
Detective Chief Inspector Mark Cranwell, from the Met's Homicide and Major Crime Command, said before Friday's arrest that it appeared four or five male suspects were involved.
He added: "The suspects fled in one direction while Ayodeji went the other way before he collapsed.
"I am appealing to anyone who was in the area on Sunday afternoon and saw this attack, or the events surrounding the attack, to come forward and speak to police.
"This includes trying to establish if anyone was with Ayodeji when he was attacked.
"My officers are making progress as to why Ayodeji was in the area, why he came to be attacked and who was responsible for his murder, but we need information from the public to assist us in keeping the momentum of this investigation moving forward."
Mr Azeez's death was one of five fatal knife attacks in London in just over a week.
Rocky Djelal, 38, died after a daylight attack in Rotherhithe, southeast London, on Wednesday 31 October.
Jay Hughes, 15, was killed by a stab wound to the heart in Bellingham, southeast London on Thursday 1 November.
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Malcolm Mide-Madariola, 17, was stabbed outside Clapham South Tube station in southwest London on Friday 2 November.
John Ogunjobi was stabbed to death in Tulse Hill, south London on Monday 5 November.