The family of Gareth Williams's family said they were "naturally disappointed" by the conclusions of the Met Police, and said they still believe he was killed.
Gareth Williams was found in a bag in the bath at his flat in Pimlico in 2010. Pathologists said he would have suffocated within three minutes if he was alive when he got inside the holdall. None of his DNA was found on the lock on the bag and his palm prints were not found on the rim of the bath.
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The plaque at number 16 Cowley Street in Westminster marks the brown brick Georgian townhouse where Sir John lived for 31 years.
A man reportedly armed with several knives has been arrested in Whitehall on suspicion of planning a terror attack, police have said.