Police are hunting for a second suspect over the death of an 18-year-old man found with stab wounds in east London.
Israel Ogunsola was discovered wounded on Link Street, Hackney, just before 20:00 BST on Wednesday.
A 17-year-old boy has been charged with murder but police said another suspect "remains at large".
Det Ch Insp Paul Considine said the Met was trying to trace "a young black male wearing black clothing who was at the scene of the murder."
He added: "There are people in the area who know what happened that have yet to call police. Their information is vital to building a clearer picture of what took place."
Six people have been killed in shootings and stabbings in London in the past seven days, prompting the city's mayor Sadiq Khan to back the use of "targeted" stop-and-search in the capital.
The 17-year-old male, who has been charged with murder in connection with Mr Ogunsola's death, appeared at Thames Magistrates' Court on Saturday, and will next appear at the Old Bailey on Tuesday.
A second 17-year-old was arrested on Wednesday evening and has since been released on bail until mid-April.
More than 50 people have been killed in violent attacks in London since the start of the year.
On Monday the government will unveil a new strategy to tackle serious violence, including an Offensive Weapons Bill for England and Wales, with new rules on the carrying of knives and acid.