In a letter to the Home Affairs Select Committee, Theresa May said the £1,716,306 figure includes the terror suspect's legal aid costs of £647,658, as well as more than £1 million in Home Office costs for pursuing the case through the courts.
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White House budget officials outlined the information during a telephone call with reporters given on condition of anonymity.
A prison officer is to be charged with gross negligence manslaughter and misconduct in public office in relation to the death of an inmate.