Officers were called by LAS at around 11.37pm on Friday, 4 December to Clifford Road SE25, following reports of a man found collapsed in the street.
The man, aged in his 70s, was taken to hospital, where he sadly later died.
Police believe they know the identity of the deceased but are still working to inform his next of kin.
The death is being treated as unexplained at this time.
Police are keen to hear from a member of the public who reported seeing the man in the street just before he collapsed. This person was in a car and said he had seen the man fall over but then left the scene.
This person is not being treated as a suspect but could help police with their enquiries.
If you are that person, or you believe you know who they are, please call South Area CID on 07741 702 725 or 101 ref CAD 8401/4 Dec.