Further tests are to be carried out on the body of an MI6 employee found at a flat near the agency's headquarters in London.
The body of codes expert Gareth Williams, 30, was discovered by officers on Monday afternoon in the top floor flat in the upmarket Pimlico area of the British capital.
The body was found stuffed into a bag in the bath of his London government flat.
Police were alerted as Mr Williams had not been seen for some time and he had been reported missing.
Mr Williams was working for MI6, which deals with foreign espionage matters, on secondment from the Government Communications Headquarters (GCHQ), the eavesdropping service.
'It's a long-standing policy of the government not to confirm or deny any individual working for the intelligence agencies,' said a spokeswoman for the Foreign Office.
The investigation into the death is being carried out by the Homicide and Serious Crime Command, indicating that detectives do not believe the death to be related to terrorism or espionage matters.
His body may have lain undiscovered for up to a fortnight. Detectives have described the death as 'suspicious and unexplained.'
An initial post mortem to determine the cause of death proved inconclusive but it is being treated as suspicious.
Mr Williams is originally from Wales and studied at Cambridge University.
A relative, William Hughes, said he worked for GCHQ, the government's so-called listening post, for 'many years.'
But he kept quiet regarding the actual nature of his work.
'He would never talk about it and it felt rude to ask.'
