Two men and two girls will continue to be questioned today over the murder of a man who was stabbed during an apparent robbery in broad daylight.
Police and paramedics were called to Hendon in north-west London at 4.45pm on Thursday and found the 38-year-old man at the junction of Brent Street and Parson Street.
Despite their efforts he died at the scene just before 5.30pm, Scotland Yard said.
Two men aged 19 and 20 and two girls aged 16 and 17 have been arrested in connection with the incident and remain in police custody.
"At this stage, it is believed that the victim was fatally stabbed whilst he was being robbed," a spokesman said.
Police believe they know the man's identity but he has not been formally identified.
His next of kin have been informed and a post-mortem examination is due to take place.
Detective Chief Inspector Matt Bonner of the force's Homicide and Serious Crime Command, said: "This is a busy area for highway traffic and it was a bright, clear day.
"I'm certain people driving or walking through the area saw something leading up to and during the stabbing that could be of vital importance to investigators.
"I would urge those people to contact us so that we can piece together the events that led up to this murder."
Anyone with information is urged to contact police on 020 8358 0200, or Crimestoppers, anonymously, on 0800 555111.