Secret agents specialising in the "dark arts" might have tried to cover up the death of an MI6 spy found in a holdall, a coroner has heard.
Relatives believe a third party was either present when Gareth Williams died or broke into his home afterwards to destroy evidence, lawyer Anthony O'Toole said.
The family is demanding answers after Scotland Yard revealed a key line of its inquiries had been an 18-month DNA mix-up.
Mr O'Toole told a pre-inquest review that Westminster Coroner's Court must establish why there was no evidence of another person in his London apartment when he died.
He said: "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."
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