The bizarre death of MI6 codebreaker Gareth Williams has baffled investigators for more than three years.
The 31-year-old maths genius was found inside a padlocked sports holdall in a bath at a Central London safehouse in August 2010.
It is believed he had been dead for more than a week.
And yesterday it was claimed that his grieving parents, Ian and Ellen, have been prevented from finding out the truth about how he died.
The family s lawyer, Anthony O Toole, revealed that he was banned from grilling an MI6 agent during the original inquest last year.
He said he was prevented from asking a key question of Mr Williams line manager - known only as Agent G - on how secret service officers could have entered his apartment.
Mr O Toole said: I was not allowed by the coroner to say to the spook, You know how to get into the flats without keys, don t you? I was told it was contrary to national security.
He added: My suggestion is that the dark arts were involved and there was a curious lack of evidence in there, almost like it had been swept clean.
Mr O Toole spoke out as Mr Williams family rejected a statement from Scotland Yard yesterday stating that his death was probably an accident .
The claim, following an 18-month review of the investigation , contradicts the findings of last year s inquest, which pointed to the likely involvement of a third party .
Coroner Fiona Wilcox said in a narrative verdict that the death was unnatural and likely to have been criminally mediated .
She was satisfied that on the balance of probabilities that Gareth was killed unlawfully .
Rejected: The parents of MI6 employee Gareth Williams, Ian and Ellen Williams rejected a Scotland Yard statement claiming the death was accidental PA
Mr O Toole fears spies gained access to his apartment and removed crucial evidence before police found the body.
In a statement the family said: We are naturally disappointed that it is still not possible to state with certainty how Gareth died.