The man seen on CCTV is described as dark skinned, with a full beard, wearing a light baggy top with a satchel across his chest.
Detective Chief Inspector Sheila Stewart said: "It is vital we track down this man who was in the precise area at the time Mariana was attacked and killed."
More top news
Five men who died in the water off Camber Sands were friends who had arrived to spend the day at the beach together, ITV News understands.
Students in London have once again done better in their GCSEs exams than those in the rest of the country.
Two members of the cabin crew were booted off the flight after a heated row over unpacking the water bottles.