Four intelligence agents were given "public interest" anonymity as the inquest into the "highly controversial" death of an MI6 spy found in a holdall opened today.
Coroner Fiona Wilcox said "there will be a real risk of harm" to national security and international relations if some of those giving evidence about Gareth Williams are exposed.
The only confirmed member of GCHQ who can be named is Stephen Gale, Dr Wilcox said.
Evidence began with Dr Wilcox expressing sympathy to family members, who fear "some agency specialising in the dark arts" leaves them with no way of knowing how and why he died.
The discovery sparked a painstaking investigation, worldwide media frenzy and several outlandish conspiracy theories.
Mr Williams, of Anglesey, north Wales, was curled up in a large North Face holdall, sealed by a padlock, at his top-floor flat in Alderney Street.
Evidence was delayed by 50 minutes as the coroner heard behind-closed-doors submissions from lawyers for MI6.