Police investigating code-breaker's death seek mystery couple

Scotland Yard want to identify a man and a woman, both of Mediterranean appearance and aged between 20 and 30, who were let into the communal entrance of Mr Williams' flat in Pimlico, central London, late one evening in June or July. His decomposing naked body was found in a padlocked holdall in a bath in the top floor flat by officers who broke in on August 23 after Mr Williams failed to appear at work for several days.

Yesterday, officers released CCTV footage of him as they appealed for the public's help.

It showed the 30-year-old entering Holland Park Underground station at about 3pm on Saturday August 14.

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 is continuing.

A force spokesman added there was no sign of any forced entry to his flat in Alderney Street, no signs of disturbance inside, and no property was believed to be missing.

Mr Williams was days from completing a one-year secondment to the headquarters of the Secret Intelligence Service, MI6, in Vauxhall, London.

Police said he had returned from a planned holiday in the United States on Wednesday August 11 and went shopping "on a number of occasions" in the West End and Knightsbridge areas.

On Sunday August 15, he went to a cash machine and then to Harrods before CCTV images show him in Hans Crescent, heading towards Sloane Street, near the Dolce and Gabbana store, at about 2.30pm

Police said Mr Williams, who was 5ft 7in and of muscular build with short hair, was wearing a red T-shirt, beige trousers and white trainers.

Inquiry head Detective Chief Inspector Jacqueline Sebire said: "This remains a complex unexplained death inquiry."