A couple sought in connection with the death of an MI6 officer may never be traced, police have conceded.
Gareth Williams, 31, from Holyhead on Anglesey, north Wales, was found dead in a padlocked holdall in his central London flat in August.
The death remains suspicious and unexplained with no cause found.
Westminster Coroner's Court heard it was unlikely that a Mediterranean couple seen at his flats before he died would be traced.
Det Ch Insp Jackie Sebire also disclosed that more forensic tests were being carried out.
Some 40 officers working for the intelligence services have been now interviewed by detectives investigating the death.
They have been questioned by Scotland Yard's counter-terrorism command - even though the inquiry is being led by a separate team specialising in homicide.
The inquest was adjourned until 31 March.
Mr Williams, a gifted mathematician, graduated with a first class degree in maths at just 17.
He began work at the Government Communications Headquarters in Cheltenham before being seconded to MI6.