Metropolitan Police detectives have released CCTV images of two suspects involved in a machete attack on a teenager in north London.
Stefan Appleton, 18, was killed in a children's playground in Nightingale Park, Canonbury, on June 10 after suffering back and chest stab wounds. He collapsed as he tried to cycle to a relative's house and was found at Caldy Walk.
Emergency services attended the scene before he was rushed to hospital where he was later pronounced dead. A post-mortem examination will take place in due course.
Appleton had gone to the park with his friends when two youths arrived on their mopeds. Police have released an image of one of the suspects fleeing the scene.
After leaving Nightingale Road the moped turned left into Ashby Grove and then out on to Essex Road, Islington.
The moped is small and dark in colour, had a learner plate under a square vehicle registration plate and a small Perspex visor.
Detective chief inspector Chris Jones, leading the investigation for the Homicide and Major Crime Command, is appealing to the public to come forward with any information.
He said: "We are releasing this image in the hope that it will jog a memory or prick someone's conscious, to coming forward and providing information that will assist us in finding Stefan's killer(s).
"The investigation is moving at a fast pace and we are grateful for the assistance we have received so far, but I would urge everyone to look at the image and call the incident room if they recall seeing it driving erratically on the day of the murder.
"I would also appeal to anyone who knows who rides or uses a moped like this to call us. Where is it now? Has it been parked or stored somewhere?"
Witnesses or anyone with information are asked to call the incident room on 020 8345 3734 or call Crimestoppers anonymously on 0800 555 111.