Two people were killed and another two left with life-threatening injuries after a collision involving a white VW Passat and a silver Toyota Avensis in Brighton Road, Croydon, last Saturday night.
The 54-year-old male driver of the VW died at the scene and a 31-year-old female passenger in the Toyota was pronounced dead at hospital. The Toyota driver and another passenger are both critically ill in hospital. A third passenger is in a stable condition.
While officers believe they know the identities of the deceased, they are awaiting formal identification. The post-mortem examinations will be held in due course.
Anyone who witnessed the collision is asked to contact the Road Death Investigation Unit at Catford Traffic Garage on 020 8285 1574.