"Mr Williams's body was found naked at his flat in Pimlico on 23 August 2010 after colleagues raised concerns for his welfare.
"He had been on a secondment with MI6 from his job as a communications officer at the GCHQ 'listening post' in Cheltenham, Gloucestershire.
"Police discovered his body inside a zipped-up red sports holdall, in the empty bath of his bathroom.
It had taken a week for MI6 to investigate the code-breaker's disappearance, and a post-mortem examination carried out by a Home Office pathologist failed to determine the cause of death.
"During a seven-day inquest in May 2012, the question of whether Mr Williams could have padlocked himself into a bag in a bath was central.
"None of his DNA was found on the lock attached to the bag and his palm prints were not found on the rim of the bath.
"Coroner Fiona Wilcox concluded that 'most of the fundamental questions in relation to how Gareth died remain unanswered'.
"But she said he was, 'on the balance of probabilities', unlawfully killed.
"At a briefing on Wednesday, the Met Police announced the conclusion of its three-year investigation into the incident.
"Deputy Assistant Commissioner Martin Hewitt said he was satisfied it was 'theoretically possible' Mr Williams could have padlocked the bag from the inside, although 'many questions remain unanswered' as to the circumstances of his death.
"But he said there was no evidence that the MI6 officer had intended to take his own life or that his death was connected to his work"
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