A teenager said to have been attacked by a gang wielding swords and knives died from multiple stab wounds, a post-mortem examination found.
Hani Abou El Kheir, 16, was set upon on the edge of Pimlico, one of London's most affluent neighbourhoods, just before 7pm on Sunday in a suspected drugs-related attack.
Emergency services battled to save his life as he lay bleeding in Lupus Street, but he died a few hours later in hospital.
Police believe Hani, who lived on the nearby Churchill Gardens estate, was assaulted by several youths and are keeping an "open mind" regarding a motive for the attack.
No-one has been arrested, Scotland Yard said.
On Tuesday a note from his mother Pauline Hickey was left with flowers at the scene where he died.
It read: "My baby. My heart is broken. I love you so much, the pain is unbearable. Your loving mother."
Another tribute attached to a nearby bus stop was a copy of a touching note written by Hani to his mother, alongside a picture of him as a child.
It said: "Thank you for being the best mum. Love to mummy, thank you for everything. Love from Hani."
The tribute was signed from relatives including the teenager's grandparents, and cousins in Ireland.