A 41-year-old local man, believed to be the driver of the car, was arrested for grievous bodily harm at the time.
This is now being treated as a homicide investigation by Surrey and Sussex Major Crime Team working in conjunction with colleagues in West Sussex Division.
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Holly has the evening forecast for the west of the region.
Holly has the evening forecast for the east of the region.
The mental health trust Southern Health has apologised unreservedly for the catastrophic failings which led to the deaths of two patients.