Charges have been stayed against a prime suspect in one of the IRA’s most notorious atrocities in England following the disclosure of a letter from the authorities promising that he would not be prosecuted for the crime. Here, an authority on human rights looks at the background On 20 July 1982, a remote-­controlled improvised explosive device containing 20-25lbs of commercial high explosive (with wire nails as shrapnel) was detonated in Hyde Park, London, while 16 members of the Blues and Royals regiment of the Household Cavalry and their horses, accompanied by two mounted police officers, were passing en route to the Changing of the Guard. Four of the guards were killed. A further 31 people were injured. Seven horses were destroyed. The police had a prime suspect early, John