A 22-year-old man stabbed to death in London's busy Oxford Street has been named as Steven Bigby.Mr Bigby died after being attacked outside a McDonald's restaurant during the afternoon rush-hour.Police said he became embroiled in a fight with an unknown number of attackers.He was stabbed on the pavement in front of hundreds of shoppers who had jammed into the area near Oxford Circus underground station, shortly before 5pm.A bloodied four-inch knife was recovered nearby and CCTV footage seized.Paramedics tried to revive Mr Bigby at the scene before he was taken to hospital where he later died.Post-mortem test results have yet to be released but police said "the early indication is that he died from a single stab wound to the chest".Police have said tourists taking holiday snaps could hold key evidence to the stabbing.Acting Detective Chief Inspector Bob Mahoney from the Met's Homicide and Serious Crime Command, said: "In particular I am appealing for anyone who was taking photographs yesterday afternoon in Oxford Street, for any reason, to contact us."We would be very keen to see these photographs as they could hold key information. This attack took place at a peak time in one of the busiest streets in London."We are very keen to speak to anyone who was in the Oxford Street area at the time of the incident who either witnessed this violent attack or who saw people running from the area."Detectives are studying dozens of eyewitness accounts and CCTV images but photographs could be useful as it is not known how many men were involved in the row.They are also working on getting descriptions of the suspects.The killing came as new guidelines to magistrates suggested that some offenders caught carrying knives could be punished with a fine.Knife crime has blighted London in recent months - the Oxford Street murder is one of several serious stabbings in 48 hours.Two teenage boys were stabbed in Holloway, north London, on Sunday night, while 16 year-old Jimmy Mizen was slashed in the throat at a bakery in Lee, southeast of the capital.