Murder squad detectives are calling for people who attended a party at a Harlesden school to come forward after a man was shot dead outside on Sunday.
It is believed the victim attended a private birthday party at Stonebridge Primary School on Saturday night and that tickets were sold for the event. It is not yet known if the victim was invited or purchased a ticket.
There were around 150 to 200 people at the party and police are urging them to get in contact.
Officers were called at around 2.30am to reports of a shooting in Shakespeare Avenue.
A man in his 20s was taken to Central Middlesex Hospital by London Ambulance but later died.
Next of kin have been informed but police are awaiting formal identification.
A post-mortem revealed the cause of death was a single gunshot wound.
A neighbour, who lives just yards from the murder scene on the Stonebridge Estate, called for tougher sentencing for those carrying guns.
The 48-year-old father-of-three, whose cousin was shot dead on the same estate a couple of years ago, said: "Things have improved and we can't let this isolated incident bring the community down again. It does make you feel worried about your own children but you can't wrap them up in cotton wool.
"I remember when it was bad years ago and we can't let it go back to that. The law on gun crime is far too lenient. People carrying guns just get a slap on the wrist and this is not working.
"These guys are career gangsters. They should get 10 years for possession. I've seen it from the beginning and youngsters need people to talk to people who have experienced this before. People who can pass down their knowledge.
"Parents are to blame. Everything starts at home. And what is worse is to think it is my generation who are the parents to this kids.
"I lost my cousin a couple of years back to gun crime and he was in his early twenties. I have also lost friends. Gun crime has affected this whole community and it is totally unacceptable."
An incident room has opened under DCI Fiona Mallon of Operation Trident, which investigates black on black gun crime in the capital.
Anyone with information should call the incident room on 020 8733 4704 or Crimestoppers anonymously on 0800 555 111.