Coroner Fiona Wilcox said it is "unlikely" the death of Gareth Williams "will ever be satisfactorily explained" as she began her narrative verdict at Westminster Coroner's Court.
Dr Wilcox said "most of the fundamental questions in relation to how Gareth died remain unanswered" after a 21-month police inquiry and a seven day inquest into the death of the MI6 codebreaker.
Mr Williams, a 31-year-old fitness enthusiast originally from Anglesey, North Wales, was found naked, curled up in a padlocked holdall in the bath of his flat in Pimlico, central London, on August 23 2010.
Pathologists said he would have suffocated within three minutes if he was alive when he got inside the 32in (81cm) by 19in (48cm) red North Face bag. Poisoning and asphyxiation are the "foremost contenders" in solving the death riddle, they said.