Profile: MI6 spy Gareth Williams
The inquest into the death of MI6 employee Gareth Williams, whose body was found in a padlocked sports bag in his central London flat in August 2010, found that he was "on the balance of probabilities" unlawfully killed.
But what is known about the 31-year-old code-breaker - described by his family as "a very private person"?
Mr Williams, originally from Holyhead, north Wales, worked as a communications officer at government listening post GCHQ, in Cheltenham, but was on a three-year secondment to MI6 in London.
Police officers went to his MI6-owned top-floor flat at 36 Alderney Street - in a part of Pimlico described by a neighbour as "a very mixed area of bankers and politicians" - on Monday 23 August.
They went there after colleagues contacted the police earlier that day saying they had not seen Mr Williams for at least 10 days.
They found his naked body, which had been padlocked inside a zipped-up large red North Face sports holdall, in the empty bath of an ensuite bathroom of the master bedroom.
Police, who have repeatedly said the death remains "suspicious and unexplained", now believe he died in the early hours of Tuesday 16 August.
Mr Williams, a keen cyclist who often took part in road races and time trials, was brought up on the island of Anglesey and attended Bodedern High School.
A talented pupil, he graduated from Bangor University with a first class degree in maths aged 17 after beginning his university studies while at secondary school.
His maths teacher at Bodedern, Geraint Williams, has praised Gareth as an "exceptional" pupil who was "the best logician" he had met.
"If you explained something once to Gareth he remembered it, you didn't have to explain it again," he said.
"It didn't surprise me at all that he was very interested in codes and ciphers and it didn't really surprise me that he was recruited by GCHQ.
"He was definitely going to go into something like that, with his brain."
Mr Williams went on to study for a postgraduate certificate in mathematics at St Catharine's College, Cambridge, in 2000, but dropped out a year later before taking up the job at GCHQ in Cheltenham.
His boss there has spoken of him as a "world-class" intelligence officer and "something of a prodigy".
Stephen Gale said it was "quite remarkable" that Mr Williams - who joined GCHQ aged 21 - had achieved what he had at such a young age.
Mr Gale said: "Colleagues recall a young man who was very close to his father - he spoke about their climbing trips together.
"They remember him as a keen cyclist. One colleague said it was like a red bullet flying around the place."
In the days after his death, his family described Mr Williams in a statement as a "generous, loving son, brother, and friend" whose loss had devastated them.
They remembered him as "a great athlete" who "loved cycling and music", and as "a very private person".
He often returned home to Anglesey to mother Ellen and father Ian, who works at the Wylfa Nuclear Power Station.
Keith Thompson, of Holyhead Cycling Club - joined by Mr Williams at the age of 17 - said he had last seen the "lovely young man" at a club meeting on Boxing Day.
"We were club mates but Gareth wasn't the sort to go to the pub after a race, so he didn't have any close friends in the group," he said.
And a cyclist at Cambridge University's bicycle club described Mr Williams as "a shy chap" with a "peculiarly memorable laugh and smile".
Mr Williams' uncle, Anglesey councillor William Hughes, meanwhile, said his "very talented" nephew "would never talk about his work - and the family knew not to ask, really".
A neighbour in Pimlico said he and others had never seen Mr Williams, adding: "It's not like you'd tell your neighbours if you were a spy."
Police 'did wrong'
In late December 2010, police revealed some "embarrassing, hurtful and distressing" details about Mr Williams which they said was necessary in the search for evidence.
They said he owned £15,000-worth of unworn women's designer clothing, which were kept in six boxes at his flat, and that he had visited a drag cabaret in east London four days before his death and had tickets to two more.
Police said he occasionally spent between 30 minutes and an hour on bondage sites.
They also said a witness had reported seeing him in a gay bar but that they did not know for certain he was gay.
However, in April 2011 Mr Williams' close friend Sian Lloyd-Jones questioned suggestions his death was linked to his private life and called on police to broaden their inquiry.
She told the police "did wrong" by releasing information about women's clothing "but didn't reveal that there was £10,000 of mountaineering equipment as well".
Ms Lloyd-Jones said he was not gay and the women's clothes were too small for him and may have been intended for her or her sister.
Elizabeth Guthrie - the second friend to appear before the coroner - described her friendship with Mr Williams as based on their mutual love of history, art, Japanese Manga cartoons, travel and humorous anecdotes.
Ms Guthrie remembered his "brilliant sense of humour" and "enormous intellect".
She also said the women's clothing found by police "certainly would not be for him" - that he had no interest in cross-dressing and she believed he was "straight".
Mr Williams' sister, Ceri Subbe, said she believed the items of women's clothing were possibly intended as gifts.
She also told the inquest her brother's enthusiasm about his job had begun to fade.
"He disliked office culture, post-work drinks, flash car competitions and the rat race. He even spoke of friction in the office," her statement said.
Ms Subbe added that Mr Williams had "encountered more red tape than he was comfortable with" in his role.
The inquest into the death of the MI6 officer later heard he was once found tied to his bed by his former landlady in Cheltenham.
Jennifer Elliot said she once found him tied to his bedstead in his boxer shorts in what she thought was a "sexually motivated" act. She said he had called for help when he could not untie himself.
Mr Williams returned to his flat - half a mile from MI6 headquarters on the banks of the River Thames - on Wednesday 11 August 2010 after a fly-drive holiday to the west coast of the US.
Police say he had been shopping in London's West End and Knightsbridge areas a number of times since then.
CCTV images captured on Saturday 14 August showed him entering Holland Park tube station at about 1500 BST.
On Sunday 15 August, he went to Harrods after visiting a cash machine and, at about 1430 BST, CCTV images showed him in Hans Crescent, heading towards Sloane Street, near the Dolce & Gabbana store.
A post-mortem examination and toxicology tests - which found no trace of drugs, alcohol or poison - and the police investigation have all failed to establish a cause of death.
Police believe that Mr Williams, whose family think may have been killed by an agent "specialising in the dark arts of the secret services", was helped into the bag.
Coroner Fiona Wilcox said it was unlikely he got into the bag by himself but doubted his death would ever be explained.