Officers have been investigating the car and van crash in Ferny Hill on November 6 last year at around 11.40pm.
Today (January 17), the Metropolitan Police has issued an appeal calling for witnesses to come forward.
Three passengers in the car – two teenage boys and an 18-year-old – were taken to hospital.
A fourth man in his 40s, who was the driver of the van, was also taken to hospital.
The 18-year-old teenager died in hospital two days after on November 8 last year.
One of the teenage boys suffered life-changing injuries, while the second teenage boy and the van driver’s injuries were assessed as non-life changing.
No arrests have been made and officers continue to make enquiries.
Detective Constable Pauline Redmond, from the Serious Collision Investigation Unit, said: “Our investigation into the collision continues to establish the events which led to the death of an 18-year-old man.
“We hope we can bring a measure of comfort to his family and loved ones by understanding exactly what happened.
“Our thoughts continue to be with everyone impacted by this tragic incident.
“We are appealing for anyone who was in the area on the night of the incident to come forward.
“We understand there were other vehicles using the road at the time who may have dash cam footage or further information which could aid our investigation.
“We urge them to contact us as soon as possible.”
Anybody who witnessed the incident, or who has potentially relevant footage or CCTV from the evening, should contact 101, quoting reference 9358/06NOV.
