In 1988 IRA terrorist Sean O'Callaghan walked into a police station and gave himself up. Sentenced to 539 years' imprisonment for IRA crimes including two murders and many terrorist attacks, O'Callaghan served six of those years before being released by royal prerogative.
The reason? For the previous sixteen years O'Callaghan had been the most highly placed informer within the ranks of the IRA and had fed the Irish Garda with countless pieces of invaluable information. He prevented the assassination of the Prince and Princess of Wales at a London theatre; he sabotaged operations,...