The "senseless" drive-by shooting of a man walking along a London street is being treated as a "tragic case of mistaken identity", Scotland Yard said.
Detective Chief Inspector Mark Lawson of the Homicide and Major Crime Command added that the killing was looked upon as gang-related.
Firearms officers and the London Ambulance Service were called to reports of a shooting in Church Road, Harlesden, on Wednesday at 9.58pm, where a man, believed to be in his 20s, was pronounced dead at the scene.
Mr Lawson, who is leading the investigation, said the man had suffered multiple gunshot wounds, adding that the shots appeared to have been fired from an automatic weapon.
The man responsible for the shooting is believed to have got out of a dark hatchback with the weapon, shooting the victim several times before returning to the vehicle and fleeing the scene.
Mr Lawson urged witnesses to come forward, appealing to anyone with video or photographic evidence to contact the Metropolitan Police or Crimestoppers.
"The investigation to identify and arrest the person responsible for this senseless murder is moving at a very fast pace," he said.
"Early indications are that shots were fired from an automatic weapon, although a firearm has not been recovered so we cannot speculate on the exact type.
"We do know that the victim was shot by a male who got out of a dark coloured vehicle.
"After the shooting this vehicle then travelled south along Church Street towards Harlesden town centre. I would like to hear from anyone who saw a vehicle which perhaps caught their attention."
He added that Scotland Yard was aware that details of the murder were "circulating" on social media, and called on anyone with information to call the force's incident room.
The victim's family has now been informed, but formal identification will not take place until after the post-mortem examination at Northwick Park Hospital on Friday.
Anyone who witnessed the incident or has information is asked to contact police on 0208 358 0200 or Crimestoppers anonymously on 0800 555 111.