A teenager has been arrested after a man who went to the same prep school as Princes William and Harry was killed.
Sven Badzak, 22, was repeatedly knifed in an attack in Kilburn, north west London, on Saturday.
Police say a 17-year-old youth was arrested earlier today on suspicion of murder. He remains in custody.
The victim’s mum Jasna, called on the PM, for whom she campaigned during the 2008 London mayoral race, to “help get justice for Sven”.
Yesterday, Mr Johnson responded, saying: “My thoughts are very much with her and with her family in mourning the loss of her son.
“I think that what is happening on the streets of too many of our cities is very, very sad and I want to see kids protected from some of the gang crime, the knife crime, the culture of violence they are all too often sucked up in.
A Met Police spokesman said: “Detectives investigating the fatal stabbing of 22-year-old Sven Badzak in Kilburn have made an arrest.
“A 17-year-old male was arrested on suspicion of murder on Tuesday. He remains in custody at an east London police station.”
A post-mortem conducted yesterday confirmed Mr Badzak died of multiple stab wounds.
A 16-year-old lad stabbed in the same incident was taken to hospital where he remains in a “stable” condition.
Detective Chief Inspector Mark Wrigley, said: “A young man has lost his life in the most tragic circumstances and we are doing everything we can to find those responsible.
“We have been carrying out enquiries, and after reviewing CCTV from the area, we are confident that Sven and his friend were the victims of an unprovoked assault by a group of males.
“As the group chased the pair, Sven and his friend became separated.
“Sven fell to the ground and was attacked by a number of the group. His friend was also attacked but managed to seek help in a nearby shop and remains in a stable condition in hospital.”
DCI Wrigley added: “Our thoughts are with both families of these victims and I want to assure them that we will support them throughout this investigation and that my team of highly experienced officers will be working tirelessly to locate and apprehend those responsible for this horrific attack.
“I would also appeal to anyone who was in or around the Willesden Lane and Kilburn High Road area at the time and may have witnessed this incident involving the victims and suspects to get in contact.
“If you were a road user and have dash cam fitted in your vehicle then please check this as you may have captured a part of this which could help our investigation.”
Asked what she would say to Mr Johnson, Mr Badzak’s mother, Jasna, said: “This is a child and his mother who helped you get elected. You knew Sven. You were high-fiving him as your mate.
“I want to hear from him, from [David] Cameron, from [George] Osborne.”
Sven was educated at Wetherby Preparatory School in London where William and Harry were also taught.