A close friend of MI6 worker Gareth Williams whose body was found in a locked bag in a bath has questioned suggestions his death was linked to his private life.
The body of the code-breaker, from Holyhead on Anglesey, was found in his London flat in August.
Police revealed he had £15,000 of designer women's clothes in the flat.
But Sian Lloyd-Jones denies speculation he was gay and wants police to broaden their inquiry.
Detectives say the key to the mystery lies in Mr Williams' private life.
Press speculation has centred on him dying during a "bizarre sex game gone wrong".
That speculation was fuelled last December when police revealed Mr Williams had the women's clothes and that he had visited a drag show at a cabaret club; that he was allegedly seen at a gay bar; and that had "limited" access to bondage sites on his mobile.
But an investigation by BBC Wales raises questions about the police investigation, and asks if the key to his death really does lie in his private life.
His close friend Sian Lloyd-Jones, told Week In Week Out: "I think it's really important here for everything to be investigated - absolutely everything. I think it's about time now that the investigation is broadened.
"I feel the police did wrong around Christmas time when they released information about the clothing, but didn't reveal that there was £10,000 of mountaineering equipment as well."
Ms Lloyd-Jones denies suggestions Mr Williams was gay or a cross-dresser, saying the women's clothes were too small for him, and were probably intended for her, or his sister, Ceri.
"The things that have been in the papers have been so hurtful. To read what has been written about him has completely broken my heart, and I know it would have broken Gareth's as well," she said.
Police still don't know how Mr Williams died, and are calling his death "unexplained and suspicious".
But Crispin Black, an intelligence analyst and former advisor to the government, says the most likely explanation is that Mr Williams was murdered.
"The thing has a professional air: it's neat, it's tidy, it's organised," he said.
"A bath is where you put things if you don't want any forensic residue to be left behind. Because you know where the body's been and you can clear up after it."
Mr Black also questions the ability of the investigating police to do their job properly.
Murder squad detectives have to interview Mr Williams's former colleagues at the Secret Intelligence Service (also known as MI6) and GCHQ, the agency in Cheltenham which provides intelligence and information for the government through another team of officers from counter-terrorism.
"One of the weaknesses of the investigation, is the murder squad are interviewing friends, or colleagues, at one remove," said Mr Black.
"Interrogation, even of completely innocent people, relies on nuance, checking the story over and over again, and eye contact.
"That's how policemen decide if you're telling the truth, or not. Even if interviewing colleagues to rule them out, it should be done by the people in charge of the investigation - not somebody else,."
Week In Week Out has also uncovered new information relating to a mystery couple detectives want to find.
Police are still trying to trace a couple of "Mediterranean appearance" who visited Mr Williams' London flat a month or two before his death and had a key to the property.
The Metropolitan Police wasn't prepared to discuss that but insists it's looked into all aspects of his life, and has received full co-operation from the intelligence agencies.
As yet there's still no date set for an inquest, when the full circumstances of Gareth Williams death may eventually be explained.
Week In Week Out: Death of a Welsh Spy is on BBC One Wales on Tuesday 5 April at 2235 BST - more about the programme