Officers investigating the death of British code-breaker Gareth Williams, whose decomposing body was found padlocked inside a holdall in his bath, have released CCTV footage of him as they appealed for the public's help.
Scotland Yard want to identify a man and a woman, both of Mediterranean appearance, who were let into the communal entrance of his flat in Pimlico, central London, late one evening in June or July.
A police spokesman added that no drugs, or indications of drug usage were recovered from the property.
Detective Chief Inspector Jacqueline Sebire, who is leading the inquiry for the force's Homicide and Serious Crime Command, said: "I would appeal to anyone who may have seen, or had contact with Gareth in the period between 11th and 23rd August to come forward and speak with us at the Incident Room on 020 8358 0200, or, to remain anonymous, Crimestoppers on 0800 555 111.
"This remains a complex unexplained death inquiry."
Police said post-mortem examinations found "no obvious cause of death" and initial indications from toxicology tests showed no trace of any alcohol or routine or recreational drugs. Testing for any other substance continues.
A force spokesman added there was no sign of any forced entry to his flat, no signs of disturbance inside and no property was believed to be missing.
"There is no suggestion the items within the flat were specifically posed," he said.
Officers want to trace two people, aged 20-30, who were let in to Mr Williams' block of flats in Alderney Street, Pimlico, late one evening in June or July.
As part of their appeal, Scotland Yard released CCTV images of the 30-year-old entering Holland Park Underground station at about 3pm on August 14.