FOR more than a decade, the chilling death of one MI6 codebreaker, found naked and decomposing inside a bag, has remained a mystery.
From cops concluding the scene was "probably an accident" to long held fears international enemies may have been involved, many scenarios have been floated.
An ex-intelligence officer and the wife of a Russian dissident are among those adding theories about what really happened to Gareth Williams.
The 31-year-old Welshman's body was found inside a hold all bag in his bath at his flat in central London in 2010.
Adding to the chilling scene's mystery was the bag, padlock or bath having no sign of fingerprints.
The key to the padlock was found inside the bag and underneath Gareth's body.
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Locks for his flat had also been removed and escapologists rendered the ability to padlock himself in the bag with the key under his body, impossible.
But in November 2013, cops concluded the expert code analyser's death was "probably an accident" and the investigation was closed.
Podcast's big new questions asked
Police investigating were, then and now, left baffled by Williams' death, which is explored in a new BBC Sounds podcast.
Death of a Codebreaker is presented by Dr Sian Williams and looks into a subsequent inquest and theories into what happened.
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Included in these are a new line that Williams' work uncovered some criminal activity and as a result was assassinated.
Up until this point, Williams' life had been dominated by early success, passing his GCSEs at 10, A Levels by 13 and completing a degree at 17.
He then went to work as a cryptologist for the Government Communications Headquarters (GCHQ) in Gloucestershire.
This was followed by a highly confidential secondment to the Secret Intelligence Service at MI6 in London before his death.
What led up to Williams' chilling death
Williams was last seen alive on Sunday, August 15 and was due to chair an MI6 meeting on Monday, August 16.
He was expected to meet a colleague that evening and was due to attend another meeting on Friday, August 20 - but failed to appear.
Despite his absence, MI6 only investigated his absence more than a week later, on August 23, after a call from Williams' sister.
In Death of a Codebreaker, journalist and author, Mark Hollingsworth, explained how London became home to Russian oligarchs and billionaires in the period just before Williams' death.
At the time there were concerns that hoards of cash coming into the capital was a result of money laundering.
This resulted in British security services monitoring Russian organised crimes but not investigating them.
New Russian theories proposed
Former British military intelligence officer, Philip Ingram, told the podcast the Russian theory "fits the modus operandi of a number of different organised crime gangs".
"The Russian is the one I would put at the top of the pile of this investigation but there are others," he said.
"Throwing it out there, I think that he has probably been involved in an investigation that has been dealing with serious organised gangs from hostile intelligence states or hostile intelligence agencies.
Intelligence organisations in most cases know exactly what has happened but they can’t prove it in a way that would stand up in a court of law.
Former British military intelligence officer, Philip Ingram
"And doing something dramatic that sends a message like this is something that different intelligence services from hostile intelligence states will do.
Mr Ingram said when Russian agencies kill they "like to do things that send out a dramatic message".
"And, the Russians are good at doctrine all that - it’s called maskirovka, which is all about masking, it’s all about throwing people off the scent," he said.
"It’ll be very difficult to prove who did what. And without proof - intelligence organisations in most cases know exactly what has happened but they can’t prove it in a way that would stand up in a court of law."
Former KGB intelligence officer, Boris Karpichkov, went further and claimed sources Russian security service told him Williams was targeted because he was involved in an operation in 2010.
I still don’t understand how you can put yourself in this bag and even locked it.
Alexander Litvinenko's wife Marina
That investigation led to the uncovering of a US-based Russian spy ring.
Marina Litvinenko, the wife of Russian security agent Alexander Litvinenko, who was poisoned and killed by the state in 2006 agreed and told the podcast Russia could be involved in Williams' death.
Litvinenko's death made global headlines and he became the first confirmed victim of lethal polonium 210-induced acute radiation syndrome.
"What happened to him (Williams), the case was absolutely extraordinary," she said.
"I still don’t understand how you can put yourself in this bag and even locked it."
Detectives previously found no traces of poison and Williams' £500 iPhone had no data because it had been wiped on August 15.
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The heating in the flat was turned up, despite summer weather which made the body decompose faster and ruined potential evidence.
The coroner's inquest in 2012 ruled that it was "likely" that the death was a criminal act, but the Metropolitan Police later concluded Williams had acted alone, locking himself in the bag before he died.