A 16-year-old boy is in a critical condition in hospital after he and another teenager were stabbed by knifemen on mopeds.
Both youngsters were stabbed in the torso in Mountearl Gardens in Streatham, south London, on December 30 at 5.30pm, Scotland Yard said.
The second boy, 17, was treated for his injuries and has been discharged from hospital.
Scotland Yard said: "Detectives believe that the victims sustained their injuries after two mopeds each with a rider and pillion passenger approached them. The pillion passengers then attacked the victims before fleeing on the waiting mopeds, heading in the direction of Mount Nod Road.
"Neither of the pillion passengers is believed to have worn a helmet."
No arrests have been made and detectives have asked witnesses or anyone with information to contact Lambeth CID on 101.