Police are hunting for a man they want to speak to in connection with the death of a 38-year-old man stabbed outside a school.
Scotland Yard has released an image of Stephen Lansana, 21, of Canning Town, following the killing of Zydrunas Laurinavicius, 38, in Hendon on July 3.
Members of the public are being advised to not approach Mr Lansana if seen, but to dial 999.
Father-of-one Mr Laurinavicius was stabbed to death outside a school in Parson Street during the school run and was pronounced dead at the scene at 5.28pm. A post-mortem examination gave cause of death as stab wounds to the chest.
His father, who was with him at the time, said his killers took an empty bag from him which has not been recovered.
Police are offering a reward of up to £20,000 for information leading to the identification, arrest and prosecution of the people responsible for his death.
Detective Inspector Mark Lawson, of the Homicide and Major Crime Command, said: "I would like to speak with anyone who has seen Stephen Lansana over the past three weeks. It is urgent that we find him and any piece of information, however small, could be the lead we require to find him."
Four men have since been charged with murder. A 19-year-old man and teenage girls, aged 16 and 17, have also been arrested and bailed until September.
Anyone with information is asked to contact the incident room at Hendon on 020 8358 0200, or call Crimestoppers anonymously on 0800 555 111.
