Relatives of an MI6 spy found in a holdall are to demand to find out if he was killed by secret services as an inquest opens.
Fellow agents, police and friends are giving evidence about Gareth Williams in a bid to help a coroner solve the 21-month mystery.
Family members fear "some agency specialising in the dark arts" leaves them with no way of knowing how and why he died, and Scotland Yard has drawn a blank in its bid to explain whether he died at the hands of a third party.
Relatives believe someone was either present when he died or broke into his home afterwards to destroy evidence.
Coroner Fiona Wilcox, who has already expressed frustration at police over DNA errors, is expected to hear from 30 witnesses over five days.
She says that whether Mr Williams was alive inside the bag and locked it himself "was at the very heart of this inquiry".
The naked and decomposing body of Mr Williams, 31, was found in the bath of his home in Pimlico, central London, in August 2010.
Mr Williams, of Anglesey, North Wales, was found in a large North Face holdall, sealed by a padlock, at his top-floor flat in Alderney Street.
A battery of post-mortem tests failed to determine how he died and police originally found it would have been impossible for him to have locked himself inside.
Family lawyer Anthony O'Toole has said the inquest at Westminster Coroner's Court must establish why there was no evidence of another person in his London apartment. He told a pre-inquest review: "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 those dark arts."