London - An inquest resumed on Monday into the mysterious death of a British spy whose naked body was found padlocked in a bag at his home two years ago.
The decomposing remains of Gareth Williams, 31, were discovered in August 2010 in a holdall in the bath at his London home, near the headquarters of Britain's MI6 external intelligence service, where he worked.
His family believe secret agents versed in the "dark arts" tried to cover up his death, but Scotland Yard detectives have found no evidence that anyone else had been with Williams in his flat at the time of his death.
Around 30 witnesses are expected to give evidence in the five-day inquest at Westminster Coroner's Court in London, but four intelligence agents among them were granted anonymity.
Coroner Fiona Wilcox said "there will be a real risk of harm" to national security and international relations if their identities are revealed.
The coroner said a practical demonstration of how Williams could have got into the bag and locked it by himself was "at the very heart of this inquiry", given that one suggestion is that it was part of a sadomasochistic sex ritual.
An expert consulted by police will not be asked to perform the demonstration in the courtroom "to prevent proceedings becoming ridiculous", the coroner said.
Vincent Williams, a lawyer for Scotland Yard, said a video of the demonstration would instead be shown to the court.
Anthony O'Toole, a lawyer for Williams' family, said they were anxious the video was not released to the public "to ensure that this sort of reconstruction does not become bandied around by media outlets".
Williams' sister Ceri Subbe took the stand to tell the inquest her brother was "a country boy" who found it hard to adapt to life in London.
"The job was not quite what he expected," she said, adding: "He encountered a lot more red tape than he was comfortable with".
But she insisted that although he was disillusioned with the "rat race" in London, his family had not been worried about his state of mind at the time of his death. He had been "upbeat" in their last conversation.
Asked about a report in The Sunday Times newspaper that he had told a friend he feared he was being followed just before he died, Subbe said her brother had never mentioned such concerns to her.
She also said she was not aware that he had an extensive wardrobe of female clothing in his flat and speculated it could possibly be "a gift... or collectibles".
The coroner said the clothing had an approximate value of £20 000.
Williams, believed to be a mathematics genius, was just days from completing a one-year secondment at MI6 from his job at GCHQ, Britain's electronic "listening post" which monitors communications for intelligence purposes.
O'Toole said at a pre-inquest review hearing last month that the family believe someone else was either present when he died, or broke into his home afterwards to destroy evidence.
"The impression of the family is that the unknown third party was a member of some agency specialising in the dark arts of the secret services - or evidence has been removed post-mortem by experts in the dark arts," he said.