Tourists taking holiday snaps along London's busy Oxford Street could hold pivotal evidence to the murder of a 22-year-old man who died after being stabbed in a row over a thrown drink, the police said yesterday.

The victim, named as Steven Bigby from north London, was murdered on Monday outside a McDonald's restaurant during the afternoon rush hour.

Police said Mr Bigby, who was with three companions, had became embroiled in a fight with about four other men after a drink was thrown by one of the groups at the other.

During the altercation, Mr Bigby was stabbed on the pavement in front of hundreds of shoppers who had jammed into the area near Oxford Circus underground station, shortly before 5 p.m.

Paramedics tried to revive him at the scene. He was taken to hospital but later died.

Detectives from the Metropolitan Police's Homicide and Serious Crime Command have since launched a murder inquiry. A bloodied four-inch knife was recovered nearby and CCTV footage seized.

"This attack took place at a peak time in one of the busiest streets in London," said Scotland Yard Acting Detective Chief Inspector Bob Mahoney.

"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 saw people running from the area."

Police were particularly interested in tourists who may have been taking holiday snaps.