Detectives from the Roads and Transport Police Command are appealing for witnesses following a fatal collision in Hayes.
Police were called to Lansbury Drive, Hayes at 18:28hrs on Sunday, 27 September following reports of a road traffic collision between a car and a motorcyclist.
Officers and London Ambulance Service attended and found two males from the motorcycle suffering from critical injuries.
The first male, believed to be aged 24, died at the scene a short while later.
The second male was taken by London Ambulance Service to a west London hospital where he remains in a critical condition.
The driver of the car stopped at the scene and is assisting police with their enquiries.
No arrests have been made.
Enquiries are ongoing.
Next-of-kin have been informed. A post-mortem examination will be held in due course; Formal identification awaits.
Local road closures are in effect.
Anyone who witnessed the collision is urged to call the Serious Collision Investigation Unit at Alperton on 0208-991-9555 or Crimestoppers anonymously on 0800-555-111.