Relatives of the 31-year-old codebreaker Gareth Williams said their emotions were still "very raw" following the discovery of his body in his London flat in 2010.
His family believe the maths genius was murdered by someone who specialised in "the dark arts of the secret services".
They allege that his death may have been linked to his work at MI6, where he had recently qualified for "operational deployment", and that fingerprints, DNA and other evidence was wiped from the scene in a cover-up.
Mr Williams's aunt Judith Thomas, from the village of Trearddur Bay in Anglesey, North Wales, told the London Evening Standard: "It's a distressing time for us, especially with the inquest starting.
"We could fill newspapers with words to describe Gareth. You couldn't find enough paper in this world to say how we feel about him."
Her husband Dafydd added: "Our feelings are still very raw. This was not a body in a bag - he was our nephew, a wonderful young man."
Another uncle, William Hughes, 62, a councillor from Bodedern, said the family were keen to see the end of the five-day hearing at Westminster coroner's court, which begins on Monday.
He said: "We just want all of this over and done with now."
Mr Williams was on secondment to MI6 when his body was found by police in his top-floor flat in Pimlico, west London, on Aug 23, 2010.
The spy, who had been working for GCHQ, the government listening post in Cheltenham, since leaving university, was discovered naked inside a red The North Face holdall, which was padlocked on the outside and placed in his bath.
Detectives have always said they were keeping an open mind on whether Mr Williams was murdered or died as a result of an accident, possibly during a bizarre sex game.
An interim hearing last month heard that a delay by MI6 in notifying police of his disappearance meant a post-mortem examination had been "ineffective" and the cause of his death remained unclear.
Dr Fiona Wilcox, the coroner conducting the inquest, was told that a series of errors, including a blunder over DNA found at the scene, had also hampered the inquiry.
The coroner was told there were no injuries on the body to suggest he had been in a struggle or resisted getting in the bag, while pathologists suggested it would have been difficult to place his body inside after death without leaving marks on the body.
Forensic examinations have failed to find any evidence that there was anyone else in the flat at the time.
The coroner said it was possible he had got into the bag himself and is considering ordering a live demonstration at the inquest involving getting a police expert to climb into an identical holdall.
Anthony O'Toole, representing the Williams family, told the coroner that, assuming Mr Williams could not have locked the bag himself, it suggested that a third party "specialising in the dark arts of the secret services" was responsible.
"Perhaps evidence was removed from the scene post mortem by an expert in those dark arts," he said.
Earlier this month William Hague, the Foreign Secretary, ordered that key evidence about Mr Williams's work with the British and US secret services must be must be heard in secret.