A husband is thought to have strangled his wife then hanged himself, police said.
Ambulance crews fought in vain to save the woman, aged in her 60s, and the body of the man, also in his 60s, was found elsewhere in the flat.
The drama happened on Wednesday at a property in Rugby Street, Bloomsbury, central London, Scotland Yard said.
A Yard spokesman said it was a murder investigation but at this early stage officers were not looking for anyone else in connection with the deaths.
Post-mortem examinations took place yesterday at St Pancras Mortuary and gave the causes of death as strangulation for the woman and injuries consistent with hanging for the man.
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The alarm was raised shortly before 2am on Tuesday. Some 20 people reportedly exited the building before crews arrived.