A sixteen-year-old girl was arrested on suspicion of being murdered by a 22-year-old man.
Ayodeji Habeeb Azeez was put to death in bright daylight at Anerley in southeast London this weekend.
He is one of five killed in just six days on Lawless London's streets.
Scotland Yard confirmed today that the teenage girl was arrested this morning in a house in south London on charges of murder.
Detectives believe that Ayodeji was attacked on Sunday before fleeing suspects on the street.
But officers today have asked that anyone with information investigate the terrible attack on daylight.
Detective Chief Inspector Mark Cranwell said: "This attack took place in the middle of the day in bright daylight on a residential street. It goes without saying that this incident would have been noticed in a normally quiet environment.
"Apparently, four or five male suspects were involved in the attack. Both she and Ayodeji were run by Grace Mews into Samos Road. By this time Ayodeji had been attacked. The suspects fled in one direction, while Ayodeji struck the other way before collapsing.
"I appeal to anyone who was in the area on Sunday afternoon and saw this attack or the events related to the attack to proceed and talk to the police. This includes trying to determine if someone was with Ayodeji when he was attacked.
"My officers are making progress on the question of why Ayodeji was in the area, why he was attacked and who was responsible for his murder, but we need public information to help us get the investigation underway."
It comes after detectives have been arrested. Two men, ages 18 and 21, were arrested in the hours following the stab on Sunday 4 November.
They were released under investigation.
Witnesses or individuals with information should contact the Incident Room on 020 8721 4054. To remain anonymous, call Crimestoppers on 0800 555 111.
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Earlier this week, a man was arrested in Enfield, North London, when he stabbed a man in his twenties.
In figures compiled by Anti-Knife UK, it has turned out to be the 250th death in the UK this year.
This makes the number greater than 2015 and 2016 together.