SECONDS after the key turned in the lock of the MI6 safe house, cops searching for agent Gareth Williams were hit with a gust of cloying heat.
It was a warm August day, yet someone had left the central heating on in the top-floor flat in Pimlico, central London.
Moments later, officers discovered a padlocked red North Face holdall in the bathtub with putrefying red liquid seeping from it.
Codebreaker Gareth’s naked body was found inside the 81cm by 48cm bag, which was fastened with a padlock from the outside, with its key under his right buttock.
The slight, 31-year-old maths prodigy was 5ft 7in.
It seemed impossible he had managed to get inside alone.
In single Gareth’s wardrobe were £20,000 of women’s designer clothes and shoes in his size.
Slung on the living-room chair was a bright orange wig, while a Jemma Kidd lipstick and matte foundation from Harvey Nichols were on a sofa.
And when his devices were searched, it revealed he had visited bondage websites a few times.
In what became known as the spy-in-the-bag case, Gareth’s death sparked a frenzy of lurid speculation.
Yet this week Scotland Yard finally revealed that a fresh forensic review of the case had proved fruitless.
They said they had found no new DNA samples to suggest someone else was in the flat when Gareth died, and concluded he had died alone.
Yet a 2012 inquest found his death was “unnatural and likely to have been criminally mediated”.
And in further intrigue this week it was alleged Gareth was one of the inventors of cryptocurrency Bitcoin during unrelated proceedings at the High Court.
Russian mafia
Australian computer programmer Dr Craig Wright reportedly named Gareth as a key player in Bitcoin’s creation during a separate court case in the US.
The allegation was made during a bitter legal battle between Dr Wright and pressure group the Crypto Open Patent Alliance, or COPA, which argued that Dr Wright claimed to have spoken to Gareth in 2011 — a year after he had died.
The police confirmation this week that they believe no one else was involved in Gareth’s death left some exasperated, including former Lib Dem MP Norman Baker, who has studied the case.
He said: “The key question for the Met is why, when the coroner believed that there was foul play, the police decided the opposite and are still sticking to the same story.
“Do they think the public are idiots? Why would anyone believe that?”
Peter Faulding, an expert on confined spaces who helped police with their original inquiry, said: “My belief is that the bag was placed in the bath with Gareth dead already.
“No one in their right mind believes he was on his own. It is a physical impossibility.”
If another person was involved in Gareth’s death, they would have to be a master in forensic detail.
No one in their right mind believes he was on his own. It is a physical impossibility
Peter Faulding
The warmth from the central heating made the body decompose faster, while placing the bag in the bath meant liquids draining from it would not leak into the flat below.
And no footprints or suspicious DNA were found in the flat.
Armchair detectives have a number of theories about Gareth’s death.
Some believed it was a professional Russian mafia hit or that the rogue nation’s security services — which have a long and bloody reach — had carried out an assassination.
The women’s clothes, they suggested, were a classic attempt at smearing a victim and were placed there to lay a false trail for investigators.
Others thought it was an inside job by British or US spooks after Gareth had stumbled on some state secret and was about to turn whistleblower.
And some believe he might have been killed by a lover during a bizarre sex game.
The intrigue is a long way from the little village of Valley, on the North Wales island of Anglesey, where Gareth was raised.
The son of Ian and Ellen, and brother of Ceri, he spoke Welsh as his first language.
At Ysgol Gymraeg Morswyn primary school it soon became clear he was a prodigy.
He was a really lovely young man, but wasn’t a great conversationalist
Keith Thompson
At five he was using the school computer and at ten he passed his maths GCSE.
At 13 he gained A grades in A-level maths and computer science. His maths teacher Geraint Williams said: “He was the best logician with the fastest brain I have ever met.”
Fellow pupils remembered Gareth as being “isolated” by his intellect.
Like his father, he was a keen member of Holyhead Cycling Club.
Keith Thompson, a cyclist who rode with the pair, said: “He was a really lovely young man, but wasn’t a great conversationalist.
“Gareth wasn’t the sort to go to the pub after a race.”
Securing a first in maths from Bangor University, at 18 he began a PhD at Manchester University, where he was approached by GCHQ, Britain’s cyber-defence agency, and hired as a code-breaker at its Cheltenham base, deciphering messages left on mobile phones and emails.
He found lodgings in a house in the Prestbury area of the town, and landlady Jennifer Elliot found her tenant “quiet and unassuming”.
In his decade there, he never brought anyone back and rarely went out after work except for an occasional drink with colleagues.
But at around 1.30am one night in 2009, Jennifer and her husband heard their lodger crying for help.
Entering his room, they saw Gareth in just his boxer shorts, with both hands tied to the headboard.
In a statement at his inquest, Jennifer said his hands were bound “tight enough to cut his wrists”.
She added: “My husband said, ‘What the bloody hell are you doing?’
“He said he was just messing about to see if he could get free.”
While he was not obviously aroused, the couple believed it was “more likely to be sexual rather than escapology” and that he was “very embarrassed, panicky and apologetic”.
Later in 2009 he was seconded to London to work for MI6 — the UK’s Secret Intelligence Service — for three years.
Yet Gareth failed to settle in the capital and asked for a transfer back to GCHQ.
But a week before he was due to move back to Cheltenham, he disappeared.
A diligent timekeeper, he failed to turn up for an MI6 meeting on August 16 but the alarm had not been raised until August 23 — and then it was by his family.
Gareth was a hugely talented person, and he was very modest and generous as well
Sir John Sawers
His naked and decomposing body was then found in his flat.
The temperature in the bag would have risen to 30C within three minutes.
Experts said he would have suffocated within 30 minutes.
Tests showed he had not been drinking or taking drugs.
There were no injuries to his body.
At his inquest, expert Peter Faulding said he had made 300 unsuccessful attempts to lock himself inside an identical-sized bag.
He added: “Even Harry Houdini himself wouldn’t have managed it.”
Coroner Fiona Wilcox insisted she was “satisfied on the balance of probabilities that Gareth was killed unlawfully”.
The police — who also considered it likely he had been murdered — continued their investigations.
Then came a breakthrough.
Jim Fetherstonhaugh, a retired Royal Artillery sergeant, showed it was possible to lock yourself into a similar- sized bag as the one Gareth died in.
His daughter Izzie demonstrated by pulling the zips together, leaving a gap to poke her fingers through and lock the padlock.
The Met now had to consider whether Gareth could have died in a sex game that went wrong.
Some investigating officers believed he was into “claustrophilia” — getting pleasure from being locked in confined spaces.
What is certainly true is that Gareth died after serving his country with honour.
At his funeral in North Wales, Sir John Sawers, then head of MI6, told mourners: “Gareth was a hugely talented person, and he was very modest and generous as well.
“He did really valuable work with us in the cause of national security.”
A master code-breaker, whose death will always be an enigma.
Who was Gareth Williams?
Gareth Williams was a Welsh mathematician who worked for the Government Communications Headquarters (GCHQ) and MI6.
He was found dead in August 2010, commonly referred to as “the spy in a bag”.
Born in Anglesey, Wales, on September 26, 1978, Williams was excellent at maths, passing his GCSE in the subject aged 10, and his A-levels at the age of 14.
He completed a doctorate in computer science aged 17.
He started work with GCHQ in 2001, and was placed on secondment with MI6 in London in 2009, a year before his death.