A third man has been arrested in connection with the murder of Dogan Ismail, who was stabbed to death over a BlackBerry mobile phone last month.
The 18-year-old man was arrested today on suspicion of murder and was taken to a north London police station. He remains in custody.
Ismail, 17, died from a single stab wound on 30 December at the Aylesbury Estate in Southwark, south London.
It is believed he had gone to meet a group of men on the estate who stole his BlackBerry phone in the hope of having it returned.
He was stabbed to death in front of his younger brother Orhan, who is 15. Paramedics arrived shortly afterwards but Ismail was pronounced dead at the scene.
Detective Chief Inspector Matt Bonner said "there is no evidence to suggest that this attack was gang-related and Dogan did not have any history of gang activity."
On the day of Ismail's death, a 15-year-old boy was arrested on suspicion of murder and a 39-year-old woman was arrested on suspicion of perverting the course of justice.
On 2 January, police released a CCTV image of another boy they wish to speak to in connection with the murder.
Dwanda Jallow, 15, from the Peckham area, is described as black, 5ft 5, clean shaven with cropped black hair and of slight build. He has brown eyes and speaks with a London accent.
Bonner said: "We are taking the rare step of publicising Jallow's name and image as it is critical he is found as soon as possible.
"Given an apparent close circle of friends and family who live locally, I believe that he may be residing with them seeking shelter in the hope that he remains out of sight.
"I am appealing to anyone, in particular to those who may have accommodated or are helping him at present, to look to their conscience and do the right thing and inform the police of his whereabouts. They owe it to the Ismail family."