Gareth Williams was many things to many people - a much-loved son, brother and friend, a maths genius, a keen cyclist and art lover, an elite code-breaker and intelligence officer with the secret service.
His story is as fascinating as his death is mysterious.
Mr Williams was born and raised in Valley on Anglesey, the son of Ian and Ellen, and brother of Ceri. Former classmates at Holyhead’s Ysgol Gynradd Morswyn remember his brilliance at maths which saw him pass his GCSE at the age of 10.
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He went on to Ysgol Uwchradd Bodedern where his ability astonished teachers - he did his A-levels at 14, and then graduated from Bangor University aged just 17. Aside from maths, he excelled at cycle racing, and was a star rider at Holyhead Cycling Club.
His friends describe him as a shy and modest youngster.
He studied for a PhD in computer science at the University of Manchester where his remarkable abilities came to the attention of the Government Communication Headquarters (GCHQ), the UK specialist communications and intelligence gathering organisation.
GCHQ was originally established after the First World War as the Government Code and Cypher School, and during the Second World War its work breaking Nazi codes at Bletchley Park would become legendary.
Bosses at GCHQ clearly thought Mr Williams was their man, and they paid for him to go on to study advanced mathematics at Cambridge. By 2001 he was working alongside the elite code-breakers, cryptologists and analysts at GCHQ in Cheltenham.
Though little has been revealed about the nature of his work, it is known he went on to spend time at RAF Menwith Hill North Yorkshire - a site that specialises in intercepting global communications - worked at Fort Meade in Maryland, home of the US's National Security Agency.
In 2009 he was seconded to the London headquarters of the Secret Intelligence Service, usually known as MI6, and moved to a government-rented flat in Pimlico.
By any measure this was an extraordinary life - a brilliant mathematician from a small Welsh town clearly thought highly of, and trusted by, people involved in critical and highly secret national security work.
His death would prove to be just as extraordinary.
In the summer of 2010, Mr Williams went on holiday to America, returning to London on August 11.
He was due to return to live and work in Cheltenham later that month - though his secondment had been for a period of three years it seems he wanted to leave London and return to the outdoor life in the West Country. He had already began to pack his belongings in preparation for the move.
In the days after his holiday he was captured on CCTV travelling around London on the Tube, and visiting shops in the West End and Knightsbridge - he was seen at Harvey Nichols on the 12th, at Fortnum & Mason on the 14th and then buying cakes from Harrods the following day.
He also went to a comedy club in Bethnal Green in East London to watch the transvestite show The Johnny Woo Experience.
In the early hours of August 16, his laptop had been used to access a cycling website.
But it seems his failure to return to work after his break was not noticed - or at least not reported to the police.
His body was found in his flat on August 23 after the Met were finally alerted - he was naked, and curled up inside a padlocked holdall which was in the bath tub. Keys to the padlock were under his body.
The Metropolitan Police issued a statement at the time detailing the discovery.
It said: "Mr Williams was found in his flat at Flat 4, 36 Alderney Street, Pimlico, SW1 on 23.08.10 by uniformed officers.
"There was no sign of any forced entry to the property, and no signs of disturbance inside.
"Mr Williams was found unclothed, in a zipped and padlocked red North Face holdall which was in an empty bath in the en suite bathroom.
"We do not believe there is any property missing from the flat. There is no suggestion the items within the flat were specifically posed. No drugs, or indications of drug usage were recovered."
A subsequent post-mortem examination at Westminster Mortuary established "no obvious cause of death", and toxicology tests found no trace of any alcohol or routine or recreational drugs - but "testing for any other substance" continued.
As part of their investigation, the Met appealed for information on a couple who had called at the same block of flats where Mr Williams lived earlier that summer - "Officers are also appealing for information to identify a man and a woman, both of Mediterranean appearance, aged between 20 - 30 years old, who called at 36 Alderney Street in June or July, late one evening."
Speculation, conspiracy theories, and rumours began to run wild.
In 2012 an inquest was held into Mr Williams' death.
The inquest heard that Mr Williams was a "world class" intelligence officer who rarely socialised with colleagues after work, instead preferring to take part in his passions for cycling and rock climbing, as well as indulging his love of music and the arts.
Colleagues at GCHQ dubbed him "the red bullet" as he sped around Gloucestershire roads on his bicycle.
His friends from London described him as "a laugh", as someone to watch DVDs with, or go for coffee and cake with.
The inquest also heard that police found wigs, make-up, shoes, and £20,000-worth of women’s designer clothes from top names including Stella McCartney, Chloe and Dior in his flat - many of the items were immaculately folded, and in pristine condition wrapped in tissue paper. Detectives said half of the internet use on Mr Williams' computers had been in the area of women's high fashion, including handbags, cosmetics, and gloves.
Friends and family members said they did not believe the clothes were for Mr Williams, but were probably intended as gifts.
He had taken two fashion design courses at Central St Martin's college in London without telling his bosses.
As part of the inquest, Mr Williams' computers and phones were examined - their browser histories showed bondage websites, but they made up only a "tiny" percentage of all his searches.
During the inquest it also emerged that nine computer memory sticks were found in Mr Williams' MI6 locker in London - a fact the security services did not tell the police about at the time.
One key question before the inquest was whether Mr Williams had locked himself in the bag.
Expert witness Peter Faulding said that he had tried and failed to lock the bag from inside 300 times.
"I couldn't say it's impossible, but I think even Houdini would have struggled with this one," he told the coroner.
The inquest also heard how an error in the taking of forensic samples initially led police to believe that DNA from another person had been found on Mr Williams' body - 60 friends and colleagues gave DNA samples to try to find a match, only for it to later be discovered that the DNA came from one of the forensic officers in the case.
No DNA, footprints of finger prints from Mr Williams were found on the rim of the bath in which he was found.
The cause of death could not be ascertained because of the level of decomposition by the time the body was found - even though it was summer the heating in the flat was running, and the rooms were hot.
The inquest heard the "foremost contenders" for cause of death were asphyxiation by suffocation or poisoning. No evidence of "restraint, gripping or holding" marks caused before death were found on his body.
After an eight-day hearing, the coroner of Westminster, Fiona Wilcox, delivered a narrative verdict, concluding Mr Williams' death was "criminally mediated" and on the balance of probability - not the "beyond reasonable doubt" of the criminal standard of proof - he had been "unlawfully killed".
During her verdict, the coroner rejected "suicidal intent", interest in bondage or cross-dressing, and "auto-erotic activity" as being related to Mr Williams' death.
She also concluded that despite "lots of speculation", there was no evidence his death was linked to his work for GCHQ or MI6.
The following year police announced the outcome of their inquiry - at the end of a three-year investigation the Met concluded that Mr Williams had probably locked himself in the holdall and died as a result of a tragic accident.
Scotland Yard said it could not "fundamentally and beyond doubt" rule out the possibility that a third party was involved in his death, but that the Welshman most likely died alone in his flat.
Detective Assistant Commissioner Martin Hewitt said at the time: "Despite all of this considerable effort, it is still the case that there is insufficient evidence to be definitive on the circumstances that led to Gareth's death.
"Rather, what we are left with is either individual pieces of evidence, or a lack of such evidence, that can logically support one of a number of hypotheses."
The police said forensic examination of Mr Williams' flat concluded that there was no sign of forced entry or DNA that pointed to a third party present at the time of his death.
DAC Hewitt said: "There are really three hypotheses that you can use here.
"One is that Gareth, for whatever reason, got himself into that bag and then was unable to get himself out and died as a result of that.
"One is that Gareth, with someone else, got into the bag consensually, then something went wrong and he died as a result of that.
"The third is that someone murdered Gareth by putting him in that bag. I would argue that any physical absence [of evidence of] a third party being present tends to make the hypotheses that there is a third party present less likely."
In the years since the death of Mr Williams, theories have continued to swirl around the case, not least because so many questions remain unanswered - Could he have successfully locked himself in the bag? Why was the heating turned on in the flat in the middle of August? Why were police not alerted to his disappearance sooner? Why did he have memory sticks in his work locker? Exactly what kind of work was he engaged in?
Former Russian intelligence officer Boris Karpichkov has since claimed Mr Williams was given a lethal injection in the ear and put into the holdall by Russian operatives after he learned the identity of a mole operating in GCHQ.
Others have claimed Mr Williams died during a sexual experiment or erotic game which went terribly wrong - which may or may not have involved people who have never been traced - or was killed by a lover.
Meanwhile last year a Buzzfeed News investigation reported the Welshman's work was focused on Russia, and that he was helping the American National Security Agency trace international money-laundering routes including those of Moscow-based mafia groups.
Former Detective Chief Inspector Colin Sutton, the most senior officer to go to Mr Williams' flat after the discovery of the body, told Buzzfeed he immediately suspected foul play and believed that the flat had been cleaned up to destroy evidence before the police arrived.
With the poisoning of former Russian spy Sergei Skripal and his daughter Yulia in Salisbury earlier this year, the murky world of espionage and the workings of secret services are in the minds of many people in a way such activities rarely are.
Professor Anthony Glees, director of the Centre of Security and Intelligence Studies, said the death of Mr Williams continued to fascinate because it had never been properly explained.
He said the Welshman was a brilliant mathematician working in the "beating heart" of GCHQ where the best-of-the-best worked on code-breaking, cyphers, and powerful computer algorithms - and the fact MI6 wanted him to join them showed they were interested in his expertise.
Professor Glees said there were three key issues in the incident - the computer memory sticks in Mr Williams' MI6 locker; whether the intelligence officer died by his own hand, and the lack of involvement by MI5, Britain's domestic counter-intelligence and security agency, in the investigaiton.
He said: "Memory sticks could be used to get information out of MI6 - or into it. They are absolutely forbidden. Gareth Williams would have known that if he was caught with them, it would be the end of his career - it's a sacking offence. The fact he got them past security is interesting, but it begs the question 'why'? Were they there to remove information or insert information?
"As for whether he killed himself, I just don't think that the idea that he locked himself in the bag is plausable.
"And then there is the absence of MI5, the security service. He was missing from work for a week. He is doing important work for MI6 and is unaccounted for for a week. Given his importance you would expect MI5 to be there at once. Has he been kidnapped? Has he defected? The absence of MI5 I find mind boggling."
The professor said he understood how upsetting the publicity around the death of Mr Williams must be for the family, but given the kind of work he was involved in, it had become a matter of national interest.
He said he thought it "overwhelmingly" likely that Mr Williams was being blackmailed at the time of his death - but the question was, by who?
And he said Russia, Iran, and China were all heavily involved in cyber warfare, exactly the kind of work in which the Welshman would have been involved.
He said "spooks" he had talked to referred to secrets and mysteries - secrets were to be uncovered, but mysteries could not be solved.
He said: "I don't believe in mysteries - mysteries are simply where all the secrets have not yet been uncovered, and I don't think all the secrets as far as Gareth Williams is concerned have been uncovered at all."
Perhaps those secrets will remain uncovered.
Speaking at Mr Williams' funeral his brother-in-law, Chris Subbe, recalled a night with Gareth and his sister Ceri at the Ritz Hotel in London in June 2010, two months before his death.
He said: "The world was ours for the taking."
The man from Anglesey with a love of maths and cycling lived part of his life in a world which remains unseen.
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