A fourth person has been arrested in connection with the shooting of two teenagers in Neasden.
The 16-year-old boy voluntarily attended a police station yesterday and was arrested.
Police are continuing to appeal for witnesses and information following the double shooting in Blackbird Hill, Neasden, on Saturday, just after 10.30pm.
Officers and London Ambulance attended and found two men suffering gunshot wounds to the torso.
Both victims, white males, aged 19 and 18, were taken to separate London hospitals. They are in a serious but stable condition.
Detective Inspector Mick Millar, from the MPS Shootings Team, based at West Hendon said: "The two victims were out socialising with three friends on Blackbird Hill, close to the McDonald's restaurant at around 10.30pm when the incident took place.
"We understand that the victims were approached by possibly five black youths believed to be in their teens and that a verbal confrontation took place between them.
"The suspects were aggressive towards the victims and attempted to rob them. One suspect produced a handgun and fired several shots at the victims from a close proximity.
"All five suspects then made off, two of which were on bicycles, one of these is described as a red 'BMX' type bike.
"This was a completely unprovoked attack on two individuals who were out enjoying their Saturday evening with their friends. I believe that there would have been a number of people out on the night, and I urge the to come forward and speak to us if they have any information."
Anyone with information should call police on 0208 733 4774 or Crimestoppers anonymously on 0800 555 111.