A 17-year-old boy has been stabbed to death in west London.
Police were called at 0.15am on Wednesday November 15 to reports of a fight in progress in Burket Close, Southall.
Officers and London Ambulance Service attended and found the teenager suffering injuries.
The Met Police said despite the best efforts of the emergency services he was pronounced dead at the scene. His next of kin have been informed.
Four men aged 21, 27, 31 and 71 - have been arrested on suspicion of murder. Police have yet to release their ages.
A crime scene remains in place. Enquiries into the circumstances continue.
Detective Superintendent Figo Forouzan, Head of CID in west London, said: "This is an extremely sad incident that will understandably cause concern in the community.
"I would like to reassure the community that we will carry out a thorough investigation to ensure those responsible are brought to justice.
"Whilst we have made arrests in this investigation, I would like to seek assistance from the public. I continue to appeal to anyone who has any information about how the events unfolded or anyone who may have captured the incident on their phone, dash cameras or doorbell footage to make contact with the police immediately."
Anyone with information that could assist police is asked to call 101 or ‘X’ @MetCC and quote CAD 63/15Nov. You can also provide information anonymously to the independent charity Crimestoppers on 0800 555 111.