Eleven people arrested in connection with the murder on Oxford Street have been bailed.
All of those arrested – one aged 16; three aged 17; five aged 19 and two aged 22 – have been bailed to dates in mid-January pending further investigation.
Police were called at approximately 13:45hrs on 26th December 2011 to reports of a male stabbed in Oxford Street, near the junction with Stratford Place, W1.
Officers, London Ambulance Service and London's Air Ambulance attended but he was pronounced dead at the scene.
The victim was Seydou Diarrassouba, 18, from Mitcham. Next of kin have been informed.
A post-mortem examination at Westminster Mortuary on 27th December 2011 gave the cause of death as a single stab wound to the heart.
"Our sympathy goes to the family of the victim at this time and we are appealing for witnesses to come forward,” Detective Superintendent John Sweeney, from the Homicide and Serious Crime Command, said. "We know there were a number of people filming the incident inside Footlocker and may have captured the incident or its aftermath and we are appealing for these people to contact us."
A new incident room has been opened in Hendon under Detective Chief Inspector Kevin Concannon.
Anyone who witnessed the incident or has information that may assist police should call 020 8358 0100 or speak anonymously to Crimestoppers on 0800 555 111.