Scientific experts are examining a body found by officers investigating the disappearance of former Harrods employee Egeli Rasta.
Ms Rasta's flat has been searched
The body was found on Mitcham Common, south-west London, on Sunday, after police searched ponds and wasteland where she went running.
It remains at the scene which has been sealed off while a search is conducted.
Ms Rasta, 27, was last seen leaving her Mitcham flat on 4 July, when it is thought she was going for a jog.
"Having found the body it was almost night time," said Detective Chief Inspector David Garwood.
"A forensic team will go in this morning and investigate the scene in a systematic way."
Police have until 2300 BST on Monday to interview a man in his 20s who was arrested on Thursday on suspicion of murder.
Officers had searched his home in Mitcham, an address in Edmonton, north London, and carried out a major search on Sunday across the 460-acre Mitcham Common.
More than 40 officers had been on the common making inquiries with members of the public before the body was discovered at 2030 BST.
Scotland Yard said the body had not been identified, and a post-mortem examination would be carried out.
Det Ch Insp Garwood said: "We have searched Egeli's flat and everything she would need for day-to-day life is still there - including her make-up, passport and travel documents, and bank details.
"We know she had two pairs of trainers and only one pair remains in the flat. We believe she did not return from her jog on Tuesday."
Detectives are keen to establish whether Ms Rasta had a regular route and are urging anyone who may have seen her to contact them.
She is described as tall and thin with long blonde hair and usually wore black lycra leggings and a black top.
Ms Rasta, originally from Estonia, has been living in the UK for two years and speaks good English.
On Monday 3 July she finished her last shift as a shop assistant at Harrods in Knightsbridge at 2100 BST.
The following morning she spoke to a friend on the phone and was later seen leaving her flat sometime between 1645 and 1800 BST.
She has not been seen or heard of since and was reported missing last Saturday.
Detectives revealed that before she vanished she had arranged to meet a friend at Gatwick airport on 5 July, but did not turn up.
She also failed to attend an appointment with a temping agency on 6 July.
A man who Ms Rasta had been seeing is not being treated as a suspect.