Officers investigating a fatal stabbing in west London have made a fourth arrest.
A male, aged 15 [D], was arrested on suspicion of murder on Friday, 8 March and has been taken into custody.
Three other males - aged 18 [A], 17 [B], and 15 [C] - were previously arrested on suspicion of murder and remain in custody.
Police were called at 14:14hrs on Thursday, 7 March to Lanfrey Place, West Kensington, W14, to reports of a person stabbed.
Officers, London Ambulance Service and London's Air Ambulance attended the scene.
A male, aged 17, was found with stab injuries to the chest.
He was taken to a central London hospital where he died a short time later.
Officers believe they know the identity of the victim, however formal identification awaits. His family are aware.
A post-mortem examination will take place in due course.
Detectives from the Homicide and Major Crime Command are investigating.
Chief Superintendent Rob Jones, Central West Area Commander said: "I understand the devastating effect that this incident will have not only on the victim's loved ones, but also on the wider community.
"Our thoughts are with the victim's family at this sad time.
"A crime scene remains at Lanfrey Place, and our colleagues from the Homicide and Major Crime Command are investigating.
"There will be a heightened visible police presence in the area and local officers will also be supported by central specialist units to prevent any potential further incidents.
"Violent crime is a priority and the police, our partners and the public must continue to work together to deal with knife crime and prevent further young lives being lost.
"We can't combat knife crime alone, as a community we all have a vital role to play in tackling violent crime.
"We need to hear from anyone who has information that could either detect or prevent crime. Your information could save a life."
Any witnesses or anyone with any information is asked to call police on 101 or contact via Twitter @MetCC quoting CAD 4136/07MAR.
To give information anonymously contact Crimestoppers on 0800 555 111 or online at crimestoppers-uk.org.