Homicide detectives have named the teenager fatally stabbed after a fight in west London.
Simarjeet Singh Nangpal, 17, suffered knife wounds in Burket Close on Wednesday.
The teenager, who lived close to the crime scene, died despite paramedics battling to save him.
Four men, aged 21, 27, 31 and 71, remain in custody after being arrested on suspicion of murder.
A witness described how how the teenager was savagely beaten and stabbed after two groups clashed in the street.
The local, who did not want to be named, intervened at one stage to try and stop the violence telling the group “you are going to kill him.”
He told the Standard: "Some guys turned up in a car and they started fighting with people on the street. There was screaming and fighting. Someone shouted ‘they attacked my family’. The fighting was outside a house on Burket Close it was utter mayhem."
Another neighbour said the victim’s mother was at the scene and was screaming with grief. They said: “She was in a terrible way it was heartbreaking to see.”
Detective Inspector Martin Thorpe, from Specialist Crime South, said: “We are working around the clock to find those responsible for Simarjeet’s murder, as his family struggle to come to terms with their loss.
"Four men have been arrested and our enquiries continue. I would urge anyone with information about how the events unfolded or anyone who may have captured the incident on their phone, dash cameras or doorbell footage to please come forward.”
Detective Superintendent Figo Forouzan, Head of CID in west London, said: "Our thoughts remain with Simarjeet’s family at this extremely difficult time. No family should have to go through what they are experiencing.
"This incident will undoubtedly cause wider concern, and I want to reassure the community that we will do everything in our power to find those responsible. In the coming days you will see extra officers out on patrol in your area. Please do speak to them about any concerns you may have.”
The four suspects were arrested at the scene. Two were initially taken to hospital due to injuries they sustained prior to police arrival and have since been discharged. All four remain in police custody.
A police statement added: "Police were called at 00:15hrs on Wednesday, 15 November to reports of a fight in progress in Burket Close.
"Officers attended along with the London Ambulance Service and a teenager was found with stab injuries. Despite the best efforts of the emergency services, he was sadly pronounced dead at the scene."
