Police believe these people may have witnessed the attack

The victim, Seydou Diarrassouba, 18, was stabbed to death at the Footlocker shop on the busy shopping street.

Detectives said they are keen to speak to a number of witnesses who were present at the time inside the shop and have yet to come forward.

They released five CCTV stills - four from Footlocker and one from the nearby Forever 21 store.

Officers are trying to track the people down to confirm whether or not they witnessed the incident.

The images have been released by the Metropolitan Police

Emergency services were called to the scene at 1.45pm on December 26, but the teenager, from Mitcham, was pronounced dead at the scene.

A post-mortem examination revealed he died from a single stab wound to the heart.

Detective Chief Inspector Kevin Concannon said: "Whilst continuing to investigate this tragic stabbing last Boxing Day, it has become apparent that there are a number of witnesses to the incident who have not yet come forward.

"And it is vital we are able to speak to them so that we have a clear understanding of what happened that day.

Police at the scene where Seydou Diarrassouba was killed

"I would encourage anyone who was there and who has not yet spoken to police to contact us."

Anybody who recognises any of the individuals or has any information that may assist the investigation are urged to contact the incident room on 020 8358 0100 or, if they wish to remain anonymous, Crimestoppers on 0800 555 111.

:: A man has been charged over the murder and a number of other arrested people were released on bail.