Detectives have released the picture of a 15-year-old they want to question over the suspected murder of a teenager.
The CCTV image, filmed on a bus on Sunday, is believed to be the last sighting of Dawda Jallow, from the Peckham area of south-east London.
Police want to speak to Jallow in connection to the stabbing to death of Dogan Ismail, 17, also from Peckham.
Dogan was killed on the Aylesbury Estate in nearby Walworth on Sunday after going there with his 15-year-old brother, Orhan Ismail.
Officers confirmed on Wednesday that the brothers had gone to the notorious estate to recover a Blackberry phone stolen last Friday from Orhan.
There they encountered a group of four males and during an "altercation" the victim was fatally injured.
Detective Chief Inspector Matt Bonner of the Homicide and Serious Crime Command, leading the investigation, said: "It would appear that on the Sunday they went back onto the estate in an effort to recover that phone."
On Monday, officers took the highly unusual step of naming a youth when they appealed for help finding Jallow.
The image shows him travelling on the number 35 bus between Camberwell Green and Newington Causeway at just after 10.30pm on Sunday.
"If anyone knows him, if anyone knows where he has been staying, if anyone has any ideas that they should put him up for the night, I would urge them not to and call us instead," DCI Bonner said.
"He must be staying somewhere and so I am urging the community for their help in letting me know where that is."
Jallow is described as black, clean-shaven with cropped black afro hair, 5ft 5in and stocky for his age.
He has brown eyes and speaks with a London accent, although he is a Gambian national.
The incident happened just yards away from where 21-year-old Shaun Chambers, from Greenwich, was killed on 26 September.
Police said there was no link between the two deaths.
They also said that they did not believe Dogan's stabbing was gang-related and stressed that neither Dogan nor his brother had any connection to gangs.
Chief Superintendent John Sutherland, borough commander for Southwark, said the "horrifying proximity" was just a coincidence.
"The over-riding priority at the moment is to get justice for Dogan and his family," he added.
A post-mortem examination found that Dogan died of a single stab wound.
A 15-year-old boy was arrested on suspicion of murder and a 39-year-old woman on suspicion of perverting the course of justice. Both were bailed on Monday.
Anybody with information is asked to call the incident room on 020 8358 0200 or Crimestoppers anonymously on 0800 555 111.
In a statement released through the police, Dogan's family said: "Our beloved son, friend, cousin, nephew and grandson has been cruelly taken away from us.
"Words cannot describe how much we will miss him. We want justice for Dogan and his killer caught. Anyone with information, please tell the police."