Roads and Transport Command officers are appealing for witnesses following a fatal collision in Hounslow.
Police were called at around 09:35hrs on Tuesday, 17 January to reports of a collision in Green Lane, Hounslow between a car and two pedestrians.
Officers, the London Ambulance Service and London's Air Ambulance attended the scene. The two pedestrians, women both aged 26, were taken to a west London hospital.
Victim 1 died at hospital. Her next of kin have been informed. A post-mortem has yet to be arranged and formal identification will take place in due course.
The other woman, victim 2, remains in hospital in a stable condition.
A Range Rover did not stop at the scene, but was stopped shortly afterwards.
The driver, aged 39, was initially arrested on suspicion of causing injury by dangerous driving and taken to hospital.
He has since been discharged and taken into custody. He has been further arrested on suspicion of causing death by dangerous driving.
He has been bailed to return on a date in late April.
The Serious Collision Investigation Unit is carrying out enquiries into the circumstances of the incident.
Any witnesses or anyone with any information is asked to call the witnesses line on 0208 543 5157.
To give information anonymously contact Crimestoppers on 0800 555 111 or crimstoppers-uk.org.