An MI6 worker whose body was found in a holdall in the bath at his central London flat may have been murdered two weeks ago, police believe.
Gareth Williams, 30, was found dead in the top-floor flat in Alderney Street, Pimlico, on Monday afternoon.
Officers broke in after work colleagues said Mr Williams, from Anglesey, had not been seen for at least 10 days.
Police said post mortem tests have been inconclusive. His blood will now be tested for traces of drugs and alcohol.
The Metropolitan Police have classified the death as "suspicious and unexplained".
A spokesman said: "A post-mortem examination at Westminster Mortuary was unable to provide a cause of death and further tests will take place."
Officers entering the flat discovered a mobile phone and several mobile phone SIM cards laid out at the flat.
BBC News correspondent Jon Brain said Mr Williams worked at the headquarters of the Secret Intelligence Service (MI6) about half a mile from the flat in Vauxhall Cross.
He said it was not known what job he was doing there and that his death was not necessarily connected to it.
Mr Williams' uncle, William Hughes, told BBC News: "It was terrible when I got the phone call yesterday morning.
"Just didn't know what to believe really."
Asked about Mr Williams's career, his uncle called his nephew "very, very talented in his work".
He added: "We don't know what he was doing - never spoke about it."
The police are understood to be looking into details of Mr Williams's personal life.
'Never seen him'
Mr Williams, originally from Holyhead in Anglesey, had been working as a communication officer at government listening post at GCHQ in Cheltenham.
At the time of his death he was on secondment to MI6's headquarters on the bank of the Thames in London.
The Met said investigators were following up "several lines of inquiry" but declined to confirm the victim's occupation.
Rob Mills, 35, who lives two doors away, said the discovery was "shocking".
"I'm told the man lived at the top-floor flat but we haven't ever seen him," Mr Mills said.
"It's not like you'd tell your neighbours if you were a spy."
A spokesman for the British Foreign and Commonwealth Office, which is handling press inquiries for MI6, said: "This is a police matter.
"It is long-standing Her Majesty's Government policy not to confirm or deny any individual working for the intelligence agencies."